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258 Cards in this Set
- Front
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List the two essential fatty acids, indicate what amount of each one is
needed each day, indicate if Americans get enough DHA and EPA each day, and indicate what ratio of omega-6 to omega-3 fatty acid is ideal and whether Americans are under or over this ideal ratio. What are the health consequences of a large excess of Omega-6 fatty acid relative to Omega-3? See Slide 6. |
We have to consume lipid to get two essential fatty acids,
linoleic acid (Omega-6, RDA of 4.44 g/day) and alpha-linolenic acid (Omega-3, RDA of 2.22 g/day). The recommended intake for the two essential fatty acids gives us an omega- 6/omega-3 ratio of 2 which we think is the ideal balance. Omega-3 series Vasodilatory Anti-inflammatory Anti-aggregatory Immunostimulant Anti-arrhythm Omega 6 Vasoconstrictive Pro-inflammatory Pro-aggregatory Immunosuppressive Pro-arrhythmic |
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What lipase is found in saliva, where is it produced, what does it
hydrolyze, what products does it produce, where does it work and how well does it work? |
Lingual lipase is secreted by von Ebner’s glands in the tongue
Involved in the first phase of fat digestion Hydrolyzes medium and long-chain triglycerides Important in the digestion of milk fat in a new-born Unlike other mammalian lipases, it is highly hydrophobic and readily enters fat globules (does not need colipase or bile salts like the pancreatic lipase does) Digests 10-30% of ingested triglyceride within 20 minutes. Digestion -ptyalin (α-amylase) - identical to pancreatic amylase - cleaves α-1,4-glycosidic bonds of carbohydrates - 50% of starch, pH optimum 4-5 - functionally replaceable by pancreatic enzyme lingual lipase - triglycerides, not identical to pancreatic lipase - lower acidic optimum than amylase – remains active throughout the stomach and into the proximal duodenum - 50% of triglyceride, functionally replaceable by pancreatic enzyme - dissolves dietary constituents - increases the sensitivity of taste buds Lingual lipase and pancreatic lipase both work preferentially on medium and long-chain triglycerides and they both work the same way (hydrolyze fatty acids off the sn-1 and sn-3 position to generate a 2-monoglyceride). The big difference between the two lipases is that pancreatic lipase can not work without a colipase and bile salts while lingual lipase works without any outside help. Once the pH in the small intestine comes up to around 7, lingual lipase activity drops off to almost zero. |
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What lipase is produced by the stomach, where is it produced, what
does it hydrolyze, what products does it produce, where does it work and how well does it work? |
Gastric lipase is produced by chief cells. Lingual, gastric and
pancreatic lipases work on all three kinds of triglycerides but lingual and pancreatic lipase prefer medium and long-chain fatty acid TG’s while gastric lipase prefers short-chain and medium-chain fatty acid TG’s. The other difference is that lingual and gastric lipases cleave sn-1 and sn-3 but gastric lipase only cleaves sn-3 (produces a fatty acid and a diglyceride). |
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What two fatty acids represent about 40% of the total fatty acids
found in human milk, how does this compare to the milk of other mammals like the cow, what kind of triglyceride is formed using these two fatty acids and does this particular triglyceride have any health benefits? |
Caprylic (n-Octanic) and Capric (n-Dodecanoic) form
medium chain triglycerides(appear to promote weight loss). Easier absorption, less pancreatic stimulation, less immune suppression |
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List the six (6) lipid digestive enzymes that are produced by
pancreatic acinar cells and indicate what each enzyme does. See Summary Slide 39. |
1. Pancreatic lipase, colipase dependant. Cleaves triglycerides at sn-1 and
sn-3 only after activated by colipase. Prefers long-chain and medium-chain triglycerides. 2. Pancreatic lipase, bile salt dependent. Cleaves fatty acids off cholesterol esters, phospholipids, retinol-esters (Vitamin A esters) and triglycerides. This is a general acting esterase (will cleave any ester bond linking fatty acids to something). It does not work as well with triglycerides as the colipase dependent lipase does but it will hydrolyze all of the fatty acids off triglycerides to form glycerol and fatty acids. 3. Phospholipase A2. Cleaves fatty acids off the sn-2 position of phospholipids with a glycerol backbone. The lysophospholipid acts like a detergent to help bile salts form micelles. The second fatty acid needs to be 4 removed to get good absorption and this is done by the bile salt dependent lipase. 4. Colipase. Activated by trypsin in the gut and then it binds to the colipase dependent lipase to open up the active site. 5. Sphingomyelinase. Cleaves the phosphorylcholine off sphingomyelin to produce ceramide. 6. Ceramidase. Cleaves the fatty acid off ceramide to produce sphingosine and a fatty acid, both of which get absorbed. Beta-glucosidase action converts some of the glycolipids to ceramide which then gets processed using this enzyme. |
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What kind of gallstones did Will Sichel form and why did he form
this kind of stone? |
Will Sichel formed bilirubin stones (see medical report)
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What kind of gallstone is formed by most Americans, why does this
stone formation occur, how many Americans form gallstones that produce symptoms, what is done for patients where gallstones can’t be passed from the gallbladder and what can be done to try to prevent gallstone formation? |
Most Americans form cholesterol stones. About 80% of
gallstones are cholesterol (yellow-green stones) and the remainder are bilirubin (dark stones often called pigment stones). About 15% of Americans will have one or more stones during their lifetime. About 10% of women develop gallstones by the last trimester of pregnancy. About 50% of women over the age of 70 have gallstones. About 1 million new cases of gallstone disease are diagnosed each year. Surgery is usually required in about 1/2 of the cases. Cholesterol stones can form when the bile contains too much cholesterol, too much bilirubin, (Michel Sichel) or not enough bile salts. Stones can also form when the gallbladder does not empty as it should. Pigment (bilirubin) stones are usually the result of biliary tract infections or situations where too much bilirubin (Will Sichel) is formed. Bilirubin often acts as a seed for cholesterol stones, to get pure bilirubin stones, a very large excess of bilirubin is needed. Treatment for gallstones chenodeoxycholic acid (chenodiol; Chenix) 6 ursodeoxycholic acid (ursodiol; Actigall) statins reduce hepatic secretion of cholesterol into bile inhibition of HMG-CoA reductase: inhibit cholesterol biosynthesis increase cholesterol solubility in bile 90% of chenodiol and ursodiol are absorbed and converted to bile salts in the liver where they act to help keep cholesterol in bile in solution and they also act in the gall bladder to dissolve about 40% of the gallstones that are present in the gall bladder |
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What makes the gallbladder contract and how often do we have to
remove the gallbladder because of disease? |
Removal of the gallbladder is the most common surgery
performed in the U.S. with over 500,000 cholecystectomys performed per year. Cholecystokinin makes the gallbladder contract and the Sphincter of Oddi relax. |
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When Americans read a food label, what do they primarily look at
after checking the number of calories per serving? |
The amount of fat is always the first specific component that they
look for after total calories. |
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What is the major trans fatty acid formed by the hydrogenation of
vegetable oil and why is this particular fatty acid so bad for human health? |
80 to 90 % of trans fat is Elaidic. Oleic acid melts at 15
degrees Celsius. Elaidic will not melt until the temperature reaches 42 degrees Celsius. This difference in melting point has a major effect on membrane fluidity. Most of the naturally occurring trans fatty acid is CLA (18:2) which we think has a health benefit. Elaidic acid is the major trans fat found in hydrogenated vegetable oils and occurs in small amounts in caprine and bovine milk (very roughly 0.1 % of the 7 fatty acids)[1]. It is the trans isomer of oleic acid. Elaidic acid increases CETP activity, which in turn raises VLDL and lowers HDL cholesterol.[2] |
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Do Americans have a problem with heart disease because they eat too
much saturated fat and cholesterol each day? If this isn’t primarily responsible for heart disease in Americans, what is? |
Americans have
one of the lowest intake levels for omega-3 fatty acids and one of the highest intake levels for trans fatty acids. |
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Pancreatic lipase, colipase dependant.
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Cleaves triglycerides at sn-1 and
sn-3 only after activated by colipase. Prefers long-chain and medium-chain triglycerides. |
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Pancreatic lipase, bile salt dependent
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Cleaves fatty acids off cholesterol
esters, phospholipids, retinol-esters (Vitamin A esters) and triglycerides. This is a general acting esterase (will cleave any ester bond linking fatty acids to something). It does not work as well with triglycerides as the colipase dependent lipase does but it will hydrolyze all of the fatty acids off triglycerides to form glycerol and fatty acids. |
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Phospholipase A2
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Cleaves fatty acids off the sn-2 position of
phospholipids with a glycerol backbone. The lysophospholipid acts like a detergent to help bile salts form micelles. The second fatty acid needs to be 4 removed to get good absorption and this is done by the bile salt dependent lipase. |
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Colipase
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Activated by trypsin in the gut and then it binds to the colipase
dependent lipase to open up the active site. |
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Sphingomyelinase
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Cleaves the phosphorylcholine off sphingomyelin to
produce ceramide. |
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Ceramidase.
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Cleaves the fatty acid off ceramide to produce sphingosine
and a fatty acid, both of which get absorbed. Beta-glucosidase action converts some of the glycolipids to ceramide which then gets processed using this enzyme. |
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What is beta oxidation, where does it occur, how does it operate and
where do the fatty acids that it uses come from? |
Every cell with mitochondria will burn fatty acids except brain cells. The
beta oxidation pathway is used to burn fatty acids. Mitochondria is responsible for beta oxidation. Reaction is identical to palmitic acid synthesis, except in reverse. Very long chain FA-CAN’T undergo this, they require peroxisomes Long chain FA- can undergo this, but require carantine. Short and medium chain FA-occurs in all mitochondria including brain cells. Mitochondrial Beta Oxidation of Fatty Acids 1. Oxidation - makes use of acyl-CoA dehydrogenase, FAD => FADH2 and 2 ATP generated 2. Hydration - makes use of enoyl-CoA hydratase, addition of water 3. Oxidation - by 3-hydroxyacl-CoA dehydrogenase, NAD => NADH2 and 3 ATP generated. 4. Cleavage (thiolysis) - by acyl-CoA acetyltransferase (thiolase), CoA-SH required. Co-A is used for the thiolytic cleavage of acetic acid which generates Acetyl-CoA. |
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How are fatty acids trapped inside cells, what enzymes are used to do
this and where are these enzymes located? |
Before fatty acids can be burned in mitochondria, they have to be
activated. They also have to be activated before they can be used for lipid synthesis. Fatty acid activation occurs in the ER, the outer mitochondrial membrane, the peroxisome membrane and in the mitochondrial matrix and cytoplasm. Fatty acyl-CoA synthetase(4 different enzymes) is the enzyme that activates fatty acids. This reaction activates fatty acids so they can be used to synthesize lipids and it also traps fatty acids inside cells, once CoA is on them, they can no longer move through the plasma membrane to exit the cell. Carnitine will move these activated fatty acids into the mitochondria for beta-oxidation and FABP will move then to the ER for lipid synthesis. There is a different enzyme for the different chain length fatty acids (short, medium, long and very long). Peroxisomes have the very long and long enzymes. The ER has the medium, long and very long enzymes. The outer mitochondrial membrane has the long chain enzyme and the mitochondrial matrix has the short and medium enzymes. The cytoplasm has the short chain enzyme. |
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What compound is needed to move long-chain fatty acids into the
mitochondrial matrix, how does it work, what enzymes are needed for it to work, where is it synthesized, what 6 factors are needed for its synthesis and which of these 6 factors is most likely to be deficient in Americans? |
Long chain fatty acids can not get across the inner mitochondrial membrane.
Carnitine is used to move long chain fatty acids into the mitochondrial matrix so they can be burned. Carnitine is synthesized in the liver and kidneys from lysine. A primary carnitine deficiency occurs when synthesis or transport is defective due to gene mutation. A secondary carnitine deficiency is seen when synthesis in the liver and kidneys is lower than normal due to a lysine deficiency or another factor needed for carnitine synthesis. Carnitine synthesis requires 6 factors: Lysine, Methionine, Vitamin C, Vitamin B6, Iron and Niacin. 23% of Americans have a B6 deficiency making this the most common cause for a carnitine deficiency (incomplete answer - see LO sheet) |
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How is beta-oxidation in the mitochondria regulated?
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5
The step from acyl-CoA +Carntine to Acyl-Carntine is regulated by CPTI activity and carntine level to CONTROL fatty acid oxidation in the mitochondria. See slide for add'l details |
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What is the most common genetic defect in fatty acid oxidation, what
problems does it cause and how can it be detected at birth? |
The medium chain acyl-CoA dehydrogenase (MCAD) is probably one
of the most common inherited genetic defects in human metabolism. It is thought to be a major cause of SIDS (sudden infant death syndrome). Vomiting and lethargy after fasting in child 3-15 months of age. Newborn screening test can detect this defiency. Most biochemistry textbooks will give the normal range for serum fasting glucose as 70 to 110 mg/dl. However, most clinical labs will use 64 as the low normal. Symptoms of hypoglycemia do not start to occur until the blood glucose level drops below 60 mg/dl. A value below 45 is life threatening for an infant (SIDS). For an adult, blood glucose has to drop below 10 for death to occur. |
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What product besides acetyl-CoA is produced by the beta-oxidation of
odd chain fatty acids and what vitamin is required for the conversion of this compound to glucose in the liver? |
Odd chain fatty acids produce Propionyl-CoA as the last product of
beta-oxidation and this is converted to glucose in the liver using a B12 requiring enzyme. Only 3 enzymes require B12 for activity. Without B12, severe brain damage occurs (pernicious anemia) because branchedchain amino acids can not be metabolized in the brain. For oleic acid, the double bond is in the wrong place and in the wrong configuration (cis instead of trans). |
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What is alpha-oxidation, where does it occur, what compound is
handled by this pathway, where does this compound come from, what are the three end products that come from the alpha-oxidation of this compound, what disease occurs when alpha-oxidation is defective due to gene mutation and how often does this disease occur? |
Alpha-Oxidation occurs in peroxisomes which also have a
Beta-Oxidation pathway. There is also an Omega-Oxidation pathway which occurs in the endoplasmic reticulum. Phytanic acid is a branched chain fatty acid that beta-oxidation cannot handle. It comes from phytol. Phytol is used to form chlorophyll in plants. Large amounts are consumed each day from plant foods as well as from animals that ate plants. Only alpha-oxidation in peroxisomes can handle phytanic acid. Three compounds come from alpha oxidation including isobutryl Co-A, Acetyl Co-A, and Propinoyl Co-A. Refsum’s Disease is a rare autosomal recessive inherited disease where alpha-oxidation in peroxisomes can not occur. Accumulation of phytanic acid in nerve tissue leads to severe CNS and peripheral nerve damage. |
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Compare beta-oxidation in mitochondria with beta-oxidation in
peroxisomes. |
In peroxisomal oxidation carnitine transport is not needed.
Peroxisomes produce hydrogen peroxide, NADH and acetyl-CoA from the beta-oxidation of fatty acids. Acetyl-CoA and NADH are exported and are available for energy production. Unlike mitochondria, this beta-oxidation does not result in direct ATP production. Fatty acids have to be metabolized in brain and this is probably the way that they are handled. Peroxisomes also have enzymes to handle polyunsaturated fatty acids and only peroxisomes can handle very long chain fatty acids. |
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What is omega-oxidation, where does it occur and what two vitamins
and class of lipid are metabolized using omega-oxidation? |
It occurs in the ER by use of a mixed function oxidase. It can
produce dicarboxylic acids from FAs however most Omega oxidation is done on eicosanoids, vitamins E and A where it’s used to improve solubility for excretion in urine. You need to know that Omega Oxidation is conducted using a mixed-function oxidase in the endoplasmic reticulum. You do not need to know the other enzymes. |
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What are ketone bodies, where are they produced, what conditions are
needed for their production, what enzymes are needed for their synthesis, how and where are ketone bodies used to produce energy and what enzymes are needed for energy production from ketone bodies? |
Fatty acids are used to generate large quantities of acetyl-CoA which
drives the formation of ketone bodies. This only happens in the liver. Ketone bodies can also be formed from some of the amino acids and this can occur in any tissue. Three ketone bodies are 1.) Aceteoacetate - Acetyl-CoA + Thiolase => Acetoacetyl-CoA Acetylacetyl-CoA + HMG-CoA synthase => 8 HMG-CoA HMG-CoA + HMG-CoA lyase => acetoacetate 2.) B-hydroxybutyrate - generated from acetone by D(-)- 3-hydroxybutyrate 3.) Acetone - spontaneous generation from acetoacetate acetoacetate => acetone + CO2 3 enzymes needed for synthesis are: 1.Thiolase 2. HMG-CoA Synthetase 3. HMG-CoA Lyase You need to know that Succinyl-CoA from the TCA Cycle is needed to process ketone bodies |
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What conditions are needed for severe ketoacidosis to occur and what
kind of increase in blood and urine levels of ketone bodies occur during severe ketosis? |
Too many ketones in the blood decreases blood pH, which is why it is
called acidosis. Can lead to coma or death. INSULIN DEFICIENCY - - Activated lipolysis in adipose - Increased plasma FFA - Increased liver FA Causes accelerated ketogenesis GLUCAGON EXCESS Increased liver carnitine, decreased malonyl-CoA Activation of Carnitine Acyltransferase Causes accelerated ketogenesis Other precipitating factors -uncontrolled Diabetes Mellitus -septic shock -myocardial infarction -pregnancy |
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What 4 conditions can result in enough ketone body production to
cause death and how many Americans each year have to deal with this life-threatening acidosis? |
1. Uncontrolled diabetes mellitus-type I w/o insulin
2. Septic shock-type II diabetic 3. Myocardial infection-type II diabetic 4. Pregnancy-3% of US women develop life threatening ketoacidosis during pregnanacy Over 100,000 hospital admissions per year |
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How does glucose and the other monosaccharides get converted to
fatty acids? |
Glucose and other monosaccharides entering glycolysis in the
liver and other tissues provides the acetyl-CoA that will be used for fatty acids synthesis. If sugar intake is high, fructose also becomes an important secondary source of acetyl-CoA for fatty acid synthesis, especially in the live |
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Why is pantothenic acid a critical B-complex vitamin for fatty acid
synthesis and how often do we see a pantothenic acid deficiency in Americans? |
Pantothenic acid is vitamin B5 is component of the essential
coenzyme A I faty acid synthesis. It’s rarely deficient in the diet of Americans (only 3% have a confirmed deficiency) . |
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What is the acyl carrier protein, how is it modified to function in fatty
acid synthesis and what is its specific role in this process? |
The acyl carrier protein has a Phosphopantetheine as a prosthetic
group –attached to a carrier protein (CP) serine domain by phosphopentatheinyl transferase (PPTase). The acyl carrier protein (ACP) is used to hold fatty acids during fatty acid synthesis. |
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What compound can only be used for fatty acid synthesis and how is
this compound formed? |
Malonyl-CoA and it can only be used for faty acid synthesis
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What is the rate-limiting enzyme for fatty acid synthesis, what vitamin
does this enzyme need for activity, how often do we see a deficiency of this vitamin in Americans, where is this enzyme located and how is this enzyme regulated? Slides 18 and 19 have the summary for what is testable for the regulation of this enzyme |
Acetyl-CoA Carboxylase is the rate limiting step in fatty
acid synthesis Turns Acetyl-CoA into Malonyl-CoA 1. It needs Biotin Biotin is a prosthetic group (non-protein component of a conjugated protein that is important in the protein’s biological activity) 2. Step one: ATP-dependent carboxylation of the biotin, carried out at one active site 3. Followed by the transfer of the carboxyl group to acetyl-CoA at the second active site In the cytoplasm b. Regulation Stimulate: 1. Citrate by dephosphoylating the polymer (stimulated by insulin) 2. Insulin will activate a phosphatase to put acetyl- CoA Carboxylase in the unphosphorylated form so it can polymerize to form the most active configuration. It will also increase gene expression for this enzyme. Inhibit: 3. Palmitoyl Co-A by phosphorylating via cAMPdependent protein Kinase (induced by glucagons) a. Feeds back to transform the Acety-CoA Carboxylase from the polymerized state to the monomer state. i. Note: the polymerized state is the most active state: phosphorylation will promote depolymerization to form the monomer state 3 b. Fatty acid synthesis is diminished in a low energy state by the lack of the substrate malonyl-CoA 4. Glucagon/Epinephrine: the cyclic-AMP Dependent Kinase will phosphorylate Acetyl CaA Carboxylase. (gluc also inhibits gene expression for Acetyl-CoA Carboxylase) 5. AMP- a low energy state will activate an AMPDependent Kinase to phophorylate Acetyl-CoA caboxylase Gene Regulation 6. Insulin increases gene expression for acetyl-CoA Carboxylase a. Citrate –feed forward to promote the formation of polymerized form of acetyl- CoA carboxylase 7. Glucagon decreases gene expression for “” |
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What is the fatty acid synthetase, where is it located and what does it
do? |
Fatty acid synthase is a dimer. You do not have to know these enzyme activities. You do need to know that
this multienzyme complex operates in the cytoplasm. (incomplete answer). |
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What are the 4 steps for fatty acid synthesis and what is happening
during each step? |
Condensation
5 i. The activated acyl group will react with the CH2-carbon of the malonyl CoA, releasing Malonyl CoA’s fee COOgroup as CO2 Reduction ii. Use NADPH to reduce the B-keto group to an alchol 1. uses these enzymes: a. Malonyl/acetyl-CoA-ACP Transacylase b. Malonyl/acetyl-CoA-ACP Transacylase (on slide first is acetyl, second is malonyl c. Condensing Enzyme (B-ketoacyl Synthase) Dehydration iii. Eliminate water to create a double bond Reduction of the double bond iv. Use NADPH to create saturated fatty acyl group |
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How is fatty acid synthesis via the fatty acid synthetase regulated and
how does this regulation impact human health? |
Fatty Acid Synthase
Control is through gene expression. SREBP-1 in Liver – binds to DNA and promotes the expression of the genes that code for the four enzymes in the fatty acid synthase. Insulin – Raises SREBP-1 levels in the liver. Glucagon – Lowers SREBP-1 levels in the liver. Glucose – Raises SREBP-1 levels in the liver. Polyunsaturated Fatty Acids – Lower SREBP-1 levels in the liver. Leptin – Lowers SREBP-1 levels in Adipose Tissue and liver. |
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List the 6 enzymes that function in the citrate shuttle (slide 39) and
discuss why this shuttle plays a critical role in fatty acid synthesis. |
a. Pyruvate carboxylase (mito)
i. Turns pyruvate into oxaloacetate b. Pyruvate Dehydrogenase complex (mito) 7 i. Turns pyruvate into Acetyl CoA c. Citrate synthase + ATP (mito) i. Turns Acetyl CoA or Oxaloacetate into Citrate, Which goes from the mito into the cytosol d. ATP-Citrate lyase (cytosol) i. Turns citrate into either Acetyl Co-A or Oxaloacetate e. Malate dehydrogenase +NADH (cytosol) i. Turns Oxaloacetate into Malate f. Malic enzyme + (NADP+1 +H) (cytosol) i. Turns malate into Pyruvate and ii. Makes NADPH which helps in fatty acid synthesis 1. high pyruvate levels inhibit the malic enzyme Citrate-Malate-Pyruvate Shuttle For every acetyl-CoA moved out, 1 NADPH+H gets generated. However, 2/3 of the NADPH2 needed for fatty acid synthesis comes from the pentose phosphate pathway so this shuttle system can not be operating the way Marks shows it in Fig. 33.5 on page 609 This best shows the citrate-malate pump What I’m getting from the slides is that Malate going into the mito is necessary for citrate to come out of the cycle and Citrate coming out of the mito is necessary for Pyruvate (mainly coming from glycolysis) to come into the mitochondriaImportance: The citrate-malate-pyruvate shuttle provides cytosolic acetate units and reducing equivalents for fatty acid synthesis |
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List the 3 enzymes that form the NADPH that is needed for fatty acid
synthesis and indicate where each enzyme operates. |
The citrate shuttle produces 1/3 of the NADPH needed for fatty
acid synthesis and the rest comes from the Pentose Phosphate Pathway ENZYMES G6P Dehydrogenase—Pentose Pathway 6-Phosphogluconate Dehydrogenase -----Pentose Pathway Malic Ezyme----Citrate shuttle |
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How does palmitic acid get elongated to form stearic acid?
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Elongation means getting more than 16 C fatty acid
2 Systems Mitochondria-minor (uses Acetyl CoA to reverse Beta oxidation) Endoplasmic reticulum (dominates and better) 1. uses Malonyl CoA and Multi-Enzyme complex called Elongase |
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What are the two essential fatty acids for humans, what do they do
(why do we need them?) and what recommendation has been developed for their dietary intake? |
Linoleic Acid ( LA) Omega 6 and Alpha-lonolenic acid (ALA)
omega 3. 4.44 for omega 6 and 2.22 for omega 3The Omega-3 fatty acids are so critical for human health that we do not set a limit on their daily intake and we have minimum amounts set for EPA and DHA |
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How do we put double bonds into fatty acids and why are the omega-
3 fatty acids so important for human health? |
Cytochrome Mixed Function Oxidase system that is in smooth
endoplasmic reticulum of every cell . Desaturases introduce double bonds at specific locations in fatty acid chain. This is mportant as mammalian cells are unable to produce double bonds at certain locations. This is reason polyunsaturated fatty acids are dietary essentials( eg linoleic acid18:2 and alpha linolenic acid 18:3 are 10 essential. These two essential fatty acids are used to form eicosanoids. Eicosanoids are lipid hormones that regulate just about every metabolic process that occurs in the human body. Deficiencies are extremely rare but an imbalance between Omega-6 and Omega-3 is very common. |
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How is our current diet different from our ancestral diet and what
impact has this change in diet had on our health? |
Modern western diet is low in antioxidants, “bad” fats(omega 6) and
“bad” carbohydrates(high glycemic index). Ancestral diet-rich in antioxidants, high in omega 3,good carbohydrates(low glycemic index). CDC says that Diet is Responsible for Most (90%) of the Diseases that Occur in Humans including more heart attacks, high blood pressure, all cancers diabetes alzheimers, arthritis, autoimmune disease, epilepsy, mental disorders, learning disorders, obesity, low endurance infertility. |
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What is the USDA proposed limit for added sugar per 2,000 Calories
per day for the U.S. food label (grams per day)? What is the World Health Organizations (WHO) proposed limit for added sugar? |
40 grams per day is proposed.
There is no percent daily value because the USDA, the National Academy of Science, and the Institute of Medicine cannot agree on an upper limit WHO recommends reducing added sugar of all types to 10%of total energy consumption. Sugar is defined as all mono and disaccharides added to foods plus sugar naturally occurring in honey, syrups and fruit juice. |
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Does sugar cause health problems in humans? If it does, what
problems does it cause and what are we trying to do about it? |
Sugar
has a glycemic index of 92 when white bread is used as the testing standard (100). Sugar does not push glucose like the high glycemic index foods do: maltodextrins in sports drinks and beer-150, French bread-136, rice chex-127, crispix-124, instant rice-128, baked potato- 121, corn flakes-119 and corn chips -105. As a moderate glycemic index food, sugar is fine in moderation. |
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What has been the single most effective way to prevent childhood
obesity? |
Don’t give your children soda
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Why are we in the middle of an obesity epidemic in the U.S.?
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The sharp rise in Obesity in the U.S. directly correlates with the rise in
carbohydrate intake, fat does not make us fat, carbs make us fat. |
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What 5 tissues synthesize large amounts of triglycerides, what is the
subcellular location for triglyceride synthesis in these tissues, how do triglycerides get formed in each of these tissues, what is the rate limiting enzyme for triglyceride synthesis and how is the activity of this enzyme controlled? |
Note: most of the fatty acids that are synthesized in humans are used
to form triglycerides 1.Gut---major site of TG synth o Come from dietary lipids o Pancreatic Lipase breaks dietary fat down into fatty acids and monoglycerides (glycerol with one fatty acid still attached to it) o TO reform Triglyceride: activate two fatty acids and react with the monoglyceride 2.Liver---major site of TG synth o De novo fatty acid synthesis 2 WAYS Take Dihydroxyacetone phosphate (from glycolysis pathway/ intermediate) and use it to form glycerol or just use glycerol if available. Then use the glycerol 3 phosphate pathway to form triglycerides o Rate limiting step and committed step = DGAT (diglyceride acyl transferase) Makes the diglyceride into a triglyceride 3. and 4. Adipose tissues and Type One Muscle Cells (Slow-twitch) o Also uses glycerol 3 phosphate (using DHAP from glycolysis) o Activate the fatty acid (CoA) o Sytnthesize the triglyceride o 5. Mammary glands (in lactating women) Rate lim step= Fatty Acyl CoA synthase: traps and activates fatty acids so they can be used to synthesize triglcyerdes and other lipids. 2 This enzyme is in the ER and the Outer Mito mem. Forming the CoA thioester also traps the fatty acid in the cell Gut. Take monoglycerides and put two fatty acids in to get triglyceride (remember, the fatty acids have to be activated first - CoA derivatives). Gut has glycerol kinase because some of the triglycerides get cleaved to fatty acids and glycerol. Put two fatty acids on glycerol-3- phosphate to get phosphatidic acid. The glycerol-3-phosphate came from glycerol using glycerol kinase. Take the phosphate off and then put the last fatty acid in. Liver. Glycerol kinase (same routine as what the gut did). Remember, the liver is going to use glycerol to form glucose. It can also use the glycerol to form triglycerides. DHAP in glycolysis can be reduced to glycerol-3-phosphate. Same routine as what the gut did. Adipose tissue. No glycerol kinase, have to use DHAP. Same routine as the liver. DHAP to glycerol-3-phosphate. Glycerol-3-phosphate to phosphatidic acid. Take phosphate off (get diglyeride). Add the last fatty acid to get triglyceride. Muscle. No glycerol kinase. Do what you did in adipose tissue. Mammary Gland. Just like adipose tissue. But the really interesting thing about human mammary glands is the kind of fatty acid that is used to form the triglycerides in the milk. Palmitic acid is what fatty acid synthase forms in all tissues. But in the breast tissue, it's lauric acid (12:0). We think that this medium chain saturated fatty acid has special significance human metabolism. We used to use a lot of coconut oil in the U.S. but the scare over saturated fat stopped that. Europeans started going back to coconut oil as well as palm oil to get margarine that does not have any trans fat. Palm oil and coconut oil are very high in saturated fat and they are solids at room temperature. These oils can be blended with corn oil or soybean oil to produce margarine. We are just beginning to see some of these healthy margarines in the U.S. but Europe has been using them as their only margarine for over 10 years. Remember, we knew how bad trans fat was in the early 90's |
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List the 6 glycerophospholipids, where are these lipids formed, go
through the steps required to synthesize each one, and name the 3 glycerophospholipid that is used to form triglyceride as well as the 6 glycerophospholipids that you listed above |
1. Phosphatidlyethanolamine(PE) (cephalin) = CDPETHANOLAMINE
+ DG and also base exchange w/ PS 2. Phosphatidlyserine (PS )= CDP-DG + SERINE or base exchange with PE-serine transferase 3. Phophatidlyinositol (PI) = CDP-DG + INOSITOL 4. Phosphatidylglycerol (PG)= CDP-DG + GLYCEROL-3- PHOSPATE 5. Diphosphatidlyglycerol (DPG)(Cardiolipin) = CDP-DG +PG 6. Phosphatidylcholine (PC) (lecithin) CDP-CHOLINE + DG and SAM methylation of PE (methyltransferase) |
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Why did Colleen Lakker develop respiratory distress syndrome?
Make sure that you understand what pulmonary surfactant is, what it does, when its formed, what can replace it, what can be used to check for lung maturity and what can be used to speed up lung maturation. |
Colleen Lakker was born 6 weeks premature (born at 34 weeks
gestation), she was one of the unlucky 5% that have trouble breathing. 60% of babies born before 28 weeks gestation will develop RDS while only 5% that make it to 34 weeks gestation develop RDS. Speed up= corticosteroids Pulmonary surfactant o What it is= DPPC, LPC, phosphatidylglycerol, apoporteins and cholesterol o What it does= decrease surface tension within alveoli o When it is formed= around 34 weeks gestation is when it is completed o What can replace it= phospholipid remodeling: fatty acids in membrane can be swapped out to change the properties of the membrane: 4 Dipalmitoyllecithin in lung tissue, phospholipase A2 removes fatty acid in 2 position and replaces it with palmitic acid o What is checked for lung maturity = Lectithin/ Sphingomyelin ratio of 2 |
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List the 4 enzymes that are used for membrane lipid remodeling,
explain what each one does and indicate which one forms lung surfactant as well as releases fatty acids for eicosanoid synthesis. |
Phosphlipase A1, A2, C, D
A1-forms lysophospholipids A2-forms lysophopholipids and releases FA’s for ecoisanoid synthesis and is used to produce lungsurfactant C—forms diglyceride D—forms phosphatidic acid |
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How do we control the flow of fatty acids from the triglycerides that
are in chylomicrons and VLDL into muscle and adipose tissue? |
Lipoprotein lipase (LPL) is used to hydrolyze triglycerides in
chylomicrons and VLDL so the fatty acids can be taken up into specific tissues. |
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What does hormone-sensitive lipase do, where is it located, how is it
regulated and what regulates it? |
Hormone sensitive lipase gets FA's (and glycerol) out of adipose
tissue by hydrolyzing TG's. It is located in adipose tissue. Regulations: Receptor stimulatorso These bind to adrenergic plasma membrane receptor that activates cAMP levels by activating adenyl cyclase. Epinephrine: binds to an adrenergic plasma Norepinephrine: acts the same way Glucagon: acts the same way ACTH: acts the same way Secretin: acts the same way Vasopressin: (ADH) acts the same way Ephedrine: stimulates the Symp NS system to get norepi released adipose Inhibition- no phophorylated lipaseo Insulin- inhibits by putting phosphodiesterse in its active phosphorylated form using protein kinase B to lower cyclic AMP levles o Nicotinic acid- inhbits by stimulating phosphodiesterase activity to lower cyclic AMP levels. Also raises inhibitory G protein levels or activity to decrease receptor-mediated cyclic AMP formation o Adenosine- inhibits by binding to a receptor that inhibits adenyl cyclase which results in lower cyclic AMP levles Stimulate (primers)- Stimulate by promoting synthesis of adenyl cyclase to give better cAMP. o Glucocorticoids o GH 6 o Thyroxin Inhibits phosphodiestrase from raising cAMP levels o Caffeine o Methyxanthines o Theophylline DR. B-----Lipases are really critical enzymes and I spend quite a bit of time going over them. But if I decide to ask a question about one of them, I'm almost always disappointed. We have lingual lipase, gastric lipase, pancreatic lipase, lipoprotein lipase, hepatic lipase, acid lipase and hormonesensitive lipase. What these enzymes have in common is that they all breakdown triglycerides. But where the do it, why they do it, and how we regulate each one is very different. Hormone-sensitive lipase probably should have been called adipose lipase but that's not what happened. The breakdown of triglycerides in adipose tissue is heavily regulated. You have to know this regulation. Note: something he said he likes to test on: everything with a glycerol backbone comes from phosphatidic acid, everything with a sphingoine backbone comes from ceramine. (sp?) |
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Where are saturated fats, monounsaturated fats and polyunsaturated
fats coming from in the American diet? |
The fatty acids in our diet end up in our adipose tissue and in the
phospholipids that are in our membranes. This diet related fatty acid profile affects the functioning of our tissue. Saturated fats: butter fat, animal fat, coconut oil, palm oil, cocoa butter, palm kernel oil. |
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Why does dietary fat have a health impact on humans?
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Phospholipid Fatty Acids species affect membrane biophysics
and membrane biophysics affects protein function… e.g.When rat heart muscle is made hypoxic, the heart has a problem maintaining a normal rate of contraction and arrhythmias can occur. Changing the diet protects the rat heart from these potentially deadly changes in heart beat rhythm. |
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What is the single most effective way to prevent the development of
heart disease? |
Increase intake of Omega 3’s in diet. Increase intake of Omega 3’s in
diet. Increase intake of Omega 3’s in diet. Increase intake of Omega 3’s in diet. Increase intake of Omega 3’s in diet. Increase intake of Omega 3’s in diet. |
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What is DHA?
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DHA (Docosahexaenoic acid) is A 22 carbon 6 double bond fatty acid
that is formed from EPA. What two humans tissues does it concentrate in? DHA makes up 30% of fatty acids in brain and 60% fatty acids in retina. It plays both a compositional and functional role in brain. Why is it so critical for human infant health and are American women getting enough DHA to produce healthy babies? 8 The need for DHA is greatest during the most rapid periods of brain development. Last trimester of pregnancy through 2 years of age 70% of brain cells are developed before birth 90 % of women in the US surveyed were well below the minumum recommendation of 300 mg daily. Pregnant women reportedly have the third lowest intake of DHA in the world. |
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What is the single most effective way to prevent depression?
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Omega 3’s, Increase intake of fish(omega 3’s) in diet.
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Why do all of the animals that Americans currently eat have low
levels of Omega-3 fat? |
As soon as cattle are removed from pasture and fed corn, their
tissue levels of Omega-3 fatty acids start to drop. Every Animal and Fish on this planet will have good amounts of Omega-3 fatty acids until we feed it corn or other grains. |
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How can Americans increase their intake of omega-3 fatty acids?
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Several ways including Omega 3 supplements, Reasors Omega
3 cookies, eating fish, walnuts, etc. |
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How much Omega-3 fat should be consumed each day for good
health? |
Omega6/omega3 ratio of 4:1
2.5 g/day for maintenance Improve hearing function 5 g/d Treat chronic pain 7.5 g/d Treat neurological disease >10 g/d |
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What are the general health benefits for omega-3 fatty acids?
|
Cardiac
Reduced incidence of MI improved survival if MI occurs Gastrointestinal Improvement in Crohn’s disease & ulcerative colitis corticosteroid use in inflammatory bowel disease Rheumatology Improvement in rheumatoid arthritis symptoms corticosteroid use in rheumatoid arthritis Renal Reduced incidence of IgA nephropathy Improved outcome in renal transplant Neuropsychiatric Mood disorders Schizophrenia ADHD Depression Dementia prevention |
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What tissues synthesize cholesterol on a regular basis, how much total
cholesterol gets formed in humans each day and what tissue forms the greatest amount of cholesterol each day? |
Can
be formed in every cell except RBCs Most comes from liver o Even if cholesterol isn’t digested, chylomicrons will take up the cholesterol synthesized by the liver Some comes from skin, testes, ovaries, and adrenal glands ~ 1 gram is produced every day |
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What is the isopentenyl phosphate pathway, what organisms have this
pathway, what compounds does this pathway form in humans and what do these compounds do? |
See slide
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How much cholesterol is synthesized in peroxisomes versus the endoplasmic
reticulum and which system for cholesterol synthesis peaks at night? |
30% of the total cholesterol synthesis in the liver occurs in peroxisomes. Cytoplasmic (ER) cholesterol synthesis peaks at night while peroxisomal synthesis peaks during the day. When the liver is synthesizing fatty acids, it is also synthesizing cholesterol. You then use cytoplasmic HMG-‐CoA to get HMG-‐CoA.
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What is the rate-limiting step (enzyme along with substrate and end product)
in the synthesis of cholesterol, what enzyme forms the substrate for this key enzyme, where are these two enzymes located inside cells that synthesize cholesterol and how is the synthesis of cholesterol regulated? |
The
only Enzymes that you have to know in the cholesterol synthetic pathway are Hydroxy-‐ MethylGlutaryl-‐CoA (HMG-‐CoA) Reductase and Hydroxy-‐Methylglutaryl-‐CoA Synthase. HMG-‐CoA Synthase is mitochondrial, cytoplasmic and peroxisomal HMG-‐CoA Reductase is in peroxisomes and the endoplasmic reticulum HMG-‐CoA reductase is the rate limiting step o Turns HMG-‐CO-‐A into mevalonate o This is the enzyme statins inhibit, as well fiber will feed bacteria |
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What is used to produce cholesterol in the Fed State and what is used
during the Fasting State? |
Key
point – When the liver is synthesizing fatty acids, it’s also synthesizing cholesterol! Key Point – When the liver is synthesizing ketone bodies, its also synthesizing cholesterol 3 Cholesterol – Binds to and inhibits HMG-‐CoA Reductase. Cholesterol – Inhibits formation of SREBP-‐2. Sterol Regulatory Element Binding Protein-‐2 is going to induce the formation of messenger RNA that codes for HMG-‐CoA Reductase. Cholesterol, bile salts, oxidized cholesterol, mevalonic acid and farnesyl pyrophosphate -‐ Stimulate the degradation of HMG-‐CoA Reductase. AMP (Low Energy State) – Inhibits HMG-‐CoA Reductase through an AMP-‐ Dependent Protein Kinase action which puts phosphate on HMG-‐CoA Reductase Kinase to activate it. The reductase kinase then phosphorylates HMG-‐CoA Reductase to inactivate it. |
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What do statins do besides inhibit the synthesis of cholesterol in the liver?
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It’s
a competitive inhibitor of HMG CoA Reductase. So it reduces the production of cholesterol in the liver They reduce serum lipid levels by increasing LDL receptor synthesis,thereby reducing the formation of new arterial plaques Reduces existing plaques Reduce Inflammation (modify disease activity and organ damage by preventing endothelial activation) Raises HDL levels reduce the risk of CAD allow macrophages to remove lipid from plaques (see slide) |
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What did the Lyon Diet Heart Study tell us about the role of diet in preventing a
second heart attack in people who had already had a heart attack? |
A Mediterranean type diet reduced CVD events compared to standard lowfat
diet instructions. Further, the Lyon Diet-Heart study demonstrated that a Mediterranean type diet (one high in fruits, vegetables and linolenic acid) reduced future CVD events with significantly affecting plasma lipid levels. Combined, these observations suggest that foods contain healthful non5 nutrient components which may protect against heart disease through novel mechanisms. |
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Why are Omega-3 fatty acids so good at preventing a heart attack?
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They
improve arterial elasticity and they reduce inflammation |
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What
4 Major Classes of lipoproteins are found in human blood, where do these come from and how do they differ in their lipid composition? |
Chylomicrons
VLDL LDL HDL -‐Formed in the gut Puts everything not soluble in water from food into lymph-‐-‐blood -‐formed in the liver -‐Formed in the liver -‐Formed in the intestine and liver 40-‐500nm 20-‐22nm 9-‐15nm 1-‐5% cholesterol 50% cholesterol 25% cholesterol 1-‐10% protein 22 % protein 45% protein Apo B-‐48-‐chylomicron Apo B-‐100-‐ VLDL Apo C’s Apo E Apo B-‐100 Apo A-‐1 and 2 Apo C’s Apo E See slide if this is a mess |
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What
protein is needed for chylomicron formation, where does chylomicron synthesis occur, how are chylomicrons processed, what are chylomicron remnants, what’s in chylomicron remnants and how does the liver take up chylomicron remnants? |
Protein
in chylomicron formation= Apolipoprotein B48 Chylomicron synthesis happens in the Endoplamic reticulum and it requires phospholipids. There is no real regulation of either one. For chylomicrons, the only thing that impacts gut formation is the fat content of your last meal. Processing: Chylomicrons go into the lymph. Chylomicrons get into blood via the thoraic duct. The triglyceride gets removed by lipoprotein lipase in muscle and adipose tissue capillary beds. ApoC I, II and III have to be picked up before lipoprotein lipase processing starts. These come from HDL (maybe some from plasma also). ApoCI and II activate lipoprotein lipase, III inhibits lipoprotein lipase. Apo CII comes off the chylomicron (probably CI also) so that CIII can inhibit any further processing of chylomicrons. Once the processing has stopped, we use the term chylomicron remnant. The newly discovered liver receptor LRP sees the apoB48 and binds the remnant so it can be taken up by the liver. The liver can also see apoE. ApoE was put in chylomicrons by HDL. This appears to happen when HDL removes apoCII (and probably apoCI) to stop the hydrolysis of triglycerides in chylomicrons. Putting in apoE allows the liver to see it and take it up using the apoE receptor. We process chylomicrons very quickly. With an over night fast, the blood should be completely clear of chylomicrons. We process VLDL much more slowly. We say that only the liver can take up chylomicron |
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What
protein is needed for VLDL formation, where does VLDL synthesis occur, what happens if a high rate of triglyceride formation occurs during the synthesis of VLDL, how are VLDL particles processed, what is IDL, what does IDL form, what tissue removes most of the IDL and how is this removal of IDL accomplished? |
Protein
= Apo B-‐100 Synthesized = in the liver Regulation of Synth if the dietary intake of carbs exceeds the immediate fuel requirements.of the liver, the excess carbs are converted to triacylglycerols, along with esterified cholesterol, phospholipids, and major apoprotein apoB-‐100 and are packaged to form nascent VLDL Increased availability of fatty acids Stimulation of fatty acid synthesis Stimulation fatty acid synthesis Processing: VLDL will be secreted from the liver into the bloodstream In bloodstream they accept apoCII and apoE from circulating HDLs. Then form mature VLDL particles Will then be transported from hepatic vein to caps in skeletal m, cardiac m, adipose, and lactating mammary tissues Here LPL is activated by apoCII in the VLDL This facilitates the hydrolysis of triacylglycerol inVLDL causing the release of fatty acids and glycerol from a portion of the core triacylglycerols. Residual particles called VLDL remnants 8 1. 50% are taken up by the liver through the apoE receptors 2. 50% have additional core triacylglycerols removed to form IDL 3. Additional removal of triacylglycerols will create an LDL a. 60% of the LDL is transported back to the liver where it binds apoB-‐100 receptors b. 40% of the LDL is carried to extrahepatic tissues that contain apoB-‐100 receptors and internalize the LDL particles c. Excess/saturation of receptors will cause the nonspecific macrophages to uptake the cells near the endothelial cells i. This induces inflammation and then known to produce a cascade of atherosclerosis |
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What
is in VLDL besides cholesterol, triglycerides, phospholipids and protein? |
VLDL
is formed in the liver. Liver puts everything it has onboard that is not soluble in water into VLDL. You get carotenoids, vitamin E, coenzyme Q10, phytoestrogens, etc. Slide 56 in the Cholesterol Metabolism lecture has all of this neat stuff (didn't have the phytoestrogens though which I just now added). Slide 56 shows you LDL (LDL of course comes from VLDL after the triglyceride is removed). Liver is also storing vitamin D and vitamin K but it does not put these two fat-‐soluble vitamins into VLDL (it uses them). I wanted you to know that antioxidants get delivered to extrahepatic tissues along with cholesterol when they take up LDL using their LDL receptor. |
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What
tissue removes most of the LDL from the blood and how is this accomplished? |
Circulating
low-‐density lipoprotein (LDL) is cleared from the plasma by the liver (75%) and by extrahepatic tissues (25%). The clearance is mediated by both receptor-‐dependent (>70%) and receptor-‐independent pathways. The pathways that contribute to the clearance of LDL by LDL-‐receptor-‐independent mechanisms are poorly understood. Modifications that occur in the plasma (glycation or oxidation) may account for LDL-‐receptor-‐independent clearance mechanisms. Deficiency in the LDL receptors always results in hypercholesterolaemia. Approximately 35–50% of plasma LDL is cleared daily in normal persons. |
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What
are ACAT, LCAT and CETP and what do they do? |
ACAT-‐
LCAT—Lecithin Cholesterol Acyl Tranferase. Changes LDL from Disk to sphere formation. It turns free cholesterol to cholesterol ester. CETP—Cholesterol Ester Transfer Protein. CETP is involved in transporting CE in HDL from extra-‐hepatic tissues to the liver, either for elimination from the body in the bile or for re-‐incorporation into VLDL. This process is known as reverse cholesterol transport. CETP transfers oxidized lipids from LDL to HDL. The oxidized lipids in HDL are reduced by HDL apolipoproteins. 10 What proteins are needed for HDL formation Proteins needed for HDL formation ApoaA1-‐ synth by liver and intestine ApoA2—synth by liver i. ApoC 1 and 2 (says book and obviously necessary) What tissues produce these proteins,? Liver and Intestine Where does HDL formation occur and how does HDL get cholesterol back to the liver? Transport of HDL to the liver: b. Reverse cholesterol transport i. Cells contain protein ABCAI (ATP binding Cassette protein) pumps the cholesterol from the leaflet of the membrane to the outer leaflet, then the HDL accepts the particle ii. HDL traps the particle via LCAT (catalyzes the transfer of a fatty acid to make an esterified cholesterol) (activated by ApoA-‐I) CETP is involved in transporting CE in HDL from extra-‐hepatic tissues to the liver, either for elimination from the body in the bile or for re-‐incorporation into VLDL. This process is known as reverse cholesterol transport. The steps involved include transfer of unesterified cholesterol in cell membranes to acceptors in the extracellular space, where it is incorporated into HDL. There are at least 4 distinct pathways involving the ATP-‐binding cell membrane transporters ABCA1 or ABCG1, the HDL receptor SR-‐B1 (scavenger receptor B1) or passive diffusion. HDL is released from the SR-‐BI receptor after the cholesterol esters are transferred to the liver. |
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What
pumps phospholipids and cholesterol into nascent HDL and what activates this process? |
High-‐density
lipoprotein (HDL) particles are formed in plasma from the coalescence of individual phospholipid-‐apolipoprotein A complexes. HDL and its major apolipoprotein, apoA-‐I, are synthesized by both the liver and the intestine. The other primary apolipoprotein, apoA-‐II, is synthesized only by the liver. CETP is involved in transporting CE in HDL from extra-‐ hepatic tissues to the liver, either for elimination from the body in the bile or for re-‐incorporation into VLDL. This process is known as reverse cholesterol transport. The steps involved include transfer of unesterified cholesterol in cell membranes to acceptors in the extracellular space, where it is incorporated into HDL. There are at least 4 distinct pathways involving the ATP-‐binding cell membrane transporters ABCA1 or ABCG1, the HDL receptor SR-‐B1 (scavenger receptor B1) or passive diffusion. |
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What is metabolic syndrome and why was Ivan Applebod diagnosed with this particular
syndrome? |
Metabolic Syndrome: Disease of the Modern Era
Constellation of several risk factors that increase chance of coronary artery disease, peripheral vascular disease, stroke and type 2 diabetes. Combination of 3 or more of the following risks: Ivan has all 5 conditions that make up the Metabolic Syndrome (1) Abdominal obesity (2) Triglyceride levels above 150 mg/dL- Elevated triglycerides mean that small LDL is being produced (3) Low HDL cholesterol (4) Elevated blood pressure (>130/85 mm Hg) (5) Elevated fasting blood glucose > 100 mg/dL Aging is a major contributor: prevalence in 20-29 yr olds = 6.7%; 60-69 yr olds = 43.5% |
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Why did Ann Jeina have a heart attack and what is her doctor trying to do to prevent her
from having another one? |
Ann was diagnosed with familial hypercholesterolemia type IIA.
Hypercholesterolemia means elevated cholesterol in the blood. This elevation is due to LDL being much higher than normal. LDL is a lipoprotein. Her total cholesterol is 420 mg/dL, and her total triglyceride is 158 mg/dL. Ann’s LDL cholesterol is 356 mg/dL. Her HDL cholesterol is 32 mg/dL. Her total cholesterol and her LDL cholesterol are high enough that she was diagnosed with familial hypercholesterolemia type IIA. Ann was placed on a Step I diet (replaced by the TLC diet in 2006). She was also prescribed cholestyramine(Because Ann has a genetic defect that raises her LDL cholesterol, she was also prescribed cholestyramin) and provastatin to try to prevent another heart attack. Hyperlipoproteinemia is a metabolic disorder characterized by abnormally elevated concentrations of specific lipoprotein particles in the plasma. Hyperlipidemia (↑ plasma cholesterol and/or triglyceride) is present in all hyperlipoproteinemias. |
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What are the 6 classic hyperlipoproteinemias and which one was Ann Jeina diagnosed
with? Make sure you understand what’s wrong in patients with each type of hyperliproteinemia. |
Ann Jeina had IIA(defect in LDL receptor). See sheet for complete answer.
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What are the three causes for primary hypercholesterolemia type IIA, how common are
these genetic defects and what kind of risk does a person with one of these defects have of dying from a heart attack during their lifetime? |
1. Familial Hypercholesterolemia (type IIA)-increased LDL, 1in 500, defective LDL
receptor 2. Familial Defective ApoB100-increased LDL, 1 in 100, defective Apo B100 binding to LDLR 3. Polygenic Hypercholesterolemia-increased cholesterol, common, etiology unknown Heart disease caused by defective APOB, LDL-R results in 70% lifetime risk of MI |
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What is atherosclerosis, what are the risk factors for atherosclerosis, what risk factors are
modifiable and why is chronic infection emerging as a very important risk factor for atherosclerosis? |
Atherosclerosis is the formation of plaques in the walls of major arteries. This constricts
the lumen of the blood vessel (which impedes the flow of blood) and decreases vessel elasticity. Plaques are regions in the intima of major arteries in which smooth muscle cells, connective tissues, lipids, and debris accumulate. The last stage of plaque development often involves calcium deposition. Risk Factors: 1. Obesity 2. Decreased HDL 3. Diabetes 4. Psychological Distress 5. Family history of Heart Disease 6. Tobacco use 7. High serum homocysteine 8. High serum bilirubin 9. Elevated LDL 10. Over 50 years old 11. Poor diet 12. Sedentary lifestyle 13. Post menopause 14. High blood pressure 15. High Total Serum Cholesterol 16. Abnormalities in coagulation proteins |
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When did the age-adjusted death rate for heart disease peak in the
U.S., what was the death rate at this peak and how did this peak compare to the death date in 1900 versus 1997? |
The age-adjusted death rate for diseases of the heart peaked in 1950 at
587/100,000 . 1.3 million deaths in 1900 age-adjusted death rate of 265/100,000 versus 2.3 million deaths in 1997 age-adjusted death rate of 479/100,000 |
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Why do plaques form in artery walls and what specific lipoproteins
are responsible for this plaque formation? |
Role of the plasma lipoproteins in the development of the
atherosclerotic lesion. The development of the atherosclerotic lesion involves the interaction of lipoproteins with macrophages with the formation of foam cells, which are characteristic of early atherosclerosis. Elevated levels of three major classes of plasma lipoproteins—low-density lipoprotein (LDL), very LDL (VLDL) remnants, and lipoprotein (a) (Lp[a])—have been associated with an increased risk of early cardiovascular disease. Increased plasma concentrations of these lipoproteins are associated with increased diffusion into the vessel wall. The major atherogenic lipoprotein, LDL, requires oxidative modification to be taken up by the macrophage with the formation of foam cells. Elevated intimal levels of Lp(a) also are associated with foam cell formation. Lp(a) also may contribute to the development of atherosclerosis by competition with plasminogen for the plasminogen receptor []. Thus, the atherogenic potential of Lp(a) may result from uptake by the macrophage with foam cell formation and its thrombotic potential as a competitor of plasminogen. Foam cell formation, macrophage activation, lipid oxidation, and endothelial cell injury all lead to the release of chemotactic factors that contribute to the development of the atherosclerotic lesion. The major antiatherogenic lipoprotein, high-density lipoprotein (HDL), protects against the development of foam cells and atherosclerosis by several potential mechanisms. A major proposed mechanism is reverse cholesterol transport, whereby HDL facilitates the removal of cholesterol from the foam cells and transports this cholesterol out of the vessel wall and back to the liver where it can be removed from the 5 body. In addition, HDL may protect LDL from being oxidized in the vessel wall. Ox—oxidized. |
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Why is the HDL level the single most important factor in determine
who will have a heart attack? |
If HDL levels are high enough, foam cells can’t be formed. Other
Antiatherogenic Actions of HDL include antiinflammatory activity, antioxidative activity, antiinfectious activity, antithrombotic activity, antiapoptotic activity and vasodilatory activity. HDL also plays a role in endothelial repair. |
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Why do about 25% of current Americans have a heart attack even
though they have a completely normal lipid profile? |
Almost ¼ of the people in the U.S. that have a heart attack have
a completely normal lipid profile as we currently measure lipids. To identify more people who are at a high risk of having a heart attack, we have to measure all of the LDL and HDL subspecies. |
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What are the 6 discrete stages of pathology that occur during plaque
development and how long does it take to reach a stage where the pathology is severe enough to cause a heart attack? |
1. foam cells
2. faty streak 3. exteacelular fatty streak 4. lipid core 5. artherosclerotic plaque lipid core embedded in fibrosis 6. complicated artherosclerotic plaque(plaque rupture, thrombosis) |
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What percentage of young (12 to 14) American males have plaques in
their arteries that have reached the pathological stage where blood clots can be formed? |
8%(type III)--- Results of 1,900 autopsies performed on
U.S. males aged 12 to 14 in 1989. |
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Why do plaques rupture and cause blood clot formation?
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Inflammation was a critical step in plaque formation, it’s also a
critical step in plaque rupture. •The term vulnerable plaque is used to identify thrombosisprone plaques and plaques with a high probability of undergoing progression and becoming culprit lesions. •This schematic figure illustrates the most common type of vulnerable plaque considered responsible for acute coronary events (based on retrospective autopsy studies).1 It is characterized by a thin fibrous cap, and extensive macrophage infiltration with inflammation on or beneath the surface and a large lipid core without significant luminal narrowing.Inflammation causes plaque formation and inflammation also causes plague rupture |
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What are the surgical treatments for heart disease?
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PCTA (Percutaneous Transluminal Corornary Angioplasty)-
about 800,000 procedures a year. Stent Placement-about 1,000,000 a year. CPAG-Bypass surgery-about 700,000 year |
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What are the medical (drug) treatments for heart disease? Make
sure that you understand how each treatment works, how effective the different treatments are for lowering LDL or raising HDL and what complications can occur that would make it difficult for patients to say on one of the medical treatments. |
Lipid-modifying therapies include HMG CoA reductase inhibitors (statins),
fibrates, bile acid sequestrants (resins), nicotinic acid and its derivatives, and probucol. Statins are highly effective in lowering LDL-cholesterol and have a good tolerability profile.1-3 Data presented in this slide does not include rosuvastatin. Bile acid sequestrants are potent cholesterol-modifying agents. Adverse events such as gastrointestinal bloating, nausea and constipation limit compliance to the bile acid sequestrants.1,2 Nicotinic acid, a B-complex vitamin, is effective at reducing both LDL cholesterol and triglyceride concentrations, and increasing HDL cholesterol levels. To be effective, it must be given in pharmacologic doses. The value of nicotinic acid has been limited by the incidence of adverse events, which include flushing, skin problems, gastrointestinal distress, liver toxicity, hyperglycaemia and hyperuricemia.1,2 Fibrates are effective triglyceride-lowering and HDL-raising drugs. However, in the majority of patients they are only moderately successful in reducing LDL-cholesterol.1,2 Probucol is not available in most countries. It has only a modest LDLcholesterol- lowering effect, and there is no evidence that it reduces CHD risk and there are limited long-term tolerability data.1,2 Ezetimibe is the first of a novel class of selective cholesterol-absorption inhibitors. Ezetimibe may be useful in patients who are intolerant to other lipid-modifying therapies, and in combination with a statin in patients who 8 are intolerant to large doses of statins or need further reductions in LDL cholesterol despite maximum doses of a statin. |
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Why do fish oil supplements stabilize plaques just a well as the
statins drugs do? |
Omega 3 fatty acids decrease inflammation and platelet
aggregation. |
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What dietary factor carries the greatest risk for heart disease
development? |
For every 2% increase in trans fats a 93 % increase in CAD.
Omega-3 fatty acids are the most important dietary factor in preventing heart disease and trans fat is the most important dietary factor in causing heart disease |
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Why is going on a low fat diet useless for preventing heart disease
or for losing weight? |
Low fat diet results in decreased HDL, increased triglycerides,
decreased viamin E and essential fatty acids, increased insulin resistance. |
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What is the best kind of diet to be on to prevent heart disease?
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The Mediterranean Diet is nutrient dense, high in
antioxidants, high in omega 3 fats, low GI carbs (legumes, oats), high fruits and vegetables, low sugar, low saturated hydrogenated fats. |
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1. What are eicosanoids, what are the general functions for eicosanoids, what cells produce eicosanoids, what three fatty acids are used to form eicosanoids and which of these is the major precursor for eicosanoids in most Americans?
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Derived from polyunsaturated fatty acids with 20 carbon atoms
Found in cell membranes esterified to membrane phospholipids 1. Arachidonic acid (Omega 6 from diet) 20:4 = 20 carbons, 4 double bonds is the most common compound that produces eicosanoids 2. Dihomo-Gamma-Linolenic Acid 20:3 (Omega 6) 3. Eicosapentaenoic Acid (EPA) 20:5 (Omega 3) Common names for some eicosanoids: Prostaglandins (PG) Thromboxanes (TX) Leukotrienes (LT) Functions: Act as local hormones Participate in the inflammatory response that occurs after infection or injury • Control of bleeding through blood clot formations • Symptoms such as pain, swelling, and fever • Exaggerated ex: allergic or hypersensitive reactions Regulate smooth muscle contraction (particularly in uterus/intestine) Regulate blood pressure (constrictors and dilators, eg broncho--) Regulate sleep/wake cycle Increase water and sodium excretion in kidneys |
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What are autocoids and what fatty acid is used to form autocoids but is not used to form eicosanoids?
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DHA has 22 carbons so it can’t form eicosanoids but it does form fatty acid derivatives that have the same actions as eicosanoids. All 4 of these fatty acids are classified as autocoids.( Dihomo-gamma-linolenic-DGLA, Arachnoidic-AA, Eicosapentaenoic-EA, and Docasahexaenoic-DHA acids).
They are Endogenous substances with biological activity, local hormones that are not released or stored in glands, not circulated in the blood, they are formed at the site of action, and produce localized action. |
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3. What are resolvins and protectins, what do they do and why would a COX-2 inhibitor interfere with resolvin production?
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Resolvins are compounds that are made by the human body from the omega-3 fatty acid, eicosapentaenoic acid (EPA). They are produced by the COX-2 pathway especially in the presence of aspirin. Experimental evidence indicates that resolvins reduce cellular inflammation by inhibiting the production and transportation of inflammatory cells and inflammatory chemicals to the sites of inflammation. They are released and used immunologically by the kidneys as a tool against acute renal failure. Resolvins probably play a key role in stabilizing plaques; COX-2 inhibitors probably interfere with this function. They interfere with the function because resolvins are produced in the COX-2 pathway. Via—the vioxx disaster.
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4. What three enzymes are used to release fatty acids from membrane phospholipids for eicosanoid synthesis, where are these enzymes located, how do they work, and which one produces most of the arachidonic acid that is used for eicosanoid synthesis?
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1.) Phospholipase A2-direct release-chief enzyme responsible for releasing Arachnoidic Acid as precursor to ecosonoid synthesis.
2.) Phospholipase C-Phosphoinositol-indirect release of arachnoid acid 3.) Phospholipase D (PLD) is also involved in releasing arachidonic acid from plasma membrane phospholipids |
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5. What are the three enzyme systems that are used to produce eicosanoids, what class of eicosanoids gets formed without the action of these enzyme systems and why does this non-enzymatic formation occur?
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From arachidoinic acid---
Cyclooxygenase Produces prostaglandins and thromboxanes Lipoxygenase Creates leukotriends, lipoxins, HETE Cytochrome P450 Epoxides---diHETE and HETE Isoprostanes-These are formed by non-enzymatic lipid peroxidation catalyzed by free radicals Amplifies platelet response to other agonists. Vasoconstrictor Plasma levels 1-2 orders of magnitude > COX derived metabolites. |
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6. What does the cyclooxygenase system produce, how many COX enzymes are currently known to exist, where are these enzymes located and what does each one do?
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There are three (3) different cyclooxygenase complexes.
Cox 1 (‘the good guy’): (discovered in 1971) •Constitutively expressed •Credited for ‘house-keeping functions’ •Exception: Thromboxane synthesis in thrombocytes Cox 2 (‘the bad guy’): (discovered in 1990) •Inducible by inflammatory mediators (interleukin-1, tumor necrosis factor (TNF) •Induction inhibited by corticosteroids •Blamed for inflammation / pain / fever Cox 3 (‘the new guy’): (discovered in 2002) •Very recently discovered in dog brain (has been found in human cerebral cortex and heart muscle) •Splice variant of Cox 1 (intron 1 remains in mRNA) •Inhibited strongly by acetaminophen – which acts only weakly on Cox 1 and Cox 2 All three multienzyme complexes are located in the endoplasmic reticulum. This system produces prostaglandins, prostacyclins and thromboxanes. COX-2 is induced by inflammatory mediators and the process of inflammation. COX-1 is always present in our tissues, and is thought to mediate eicosanoid production as part of homeostasis (vasodilatory and vasoconstrictive compounds for local control) |
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What does the lipoxygenase system produce, how many lipoxygenase enzymes are currently known to exist and where are these enzymes located?
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Lipoxygenases (there is also a 15-lipoxygenase) are cytoplasmic enzymes. See slide for other details.
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8. What enzymes are needed to remove prostaglandins from the systemic circulation, and how do prostaglandins work throughout the body to regulate metabolism?
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15-prostaglandin dehydrogenase inactivates PG’s via oxidation of the C15 hydroxy group(critical for activity) to a ketone
Δ-13 reductase reduces double bond at c13 +++ Know that Prostaglandins Regulate Gene Expression. See slide for details/add'l info |
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9. How do steroids work to control inflammation, what steroids were used for Emma Wheezer and why were these particular steroids used?
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Reduced inflammatory response by
inhibiting transmigration of leukocytes attenuate the generation of inflammatory exudates Phospholipase A2 suppression COX-2 suppression Emma Wheezer was given IV dexamethasone for 10 days to treat her asthma during hospitalization and she now uses a triamcinolone acetonide inhaler to prevent another serious asthma episode. These medications inhibit production of prostaglandins due to decreased gene expression of COX-2 2- inhibit early and late manifestations of inflammation 3- which prevents chronic inflammation 4- Decrease fibroblasts which leads to inhibition of chronic inflammation (less fibrosis) and better wound healing and repair 5- Inhibits Phospholipase A2 by inducing lipocortin which leads to: •Decrease production of PAF (platelet activating factor) • Decrease Arachidonic acid which is the precursor for: * Production of prostaglandins * Leukotrienes (slow reacting substance of anaphylaxis) 6- Decrease histamine release 7- Decrease production of nitric oxide 8- Decrease production of PAF 9- Decrease the production of GM-CSF which is essential for production of: -platelets -Monocyte, neutrophil & eosinophil -RBCs |
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10. What role do eicosanoids play in inflammation?
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Eicosanoids can mediate virtually every step of inflammation.
Action Metabolite Vasoconstriction Thromboxane A2, Leukotriene C4, D4, E4 Vasodilation PGI2, PGE1, PGE2, PGD2 Increased vascul. permeab. LTC4, LTD4, LTE4 Chemotaxis, Leuko. adhesion LTB4, 5-HETE Bronchospasm Leukotriene C4, D4, E4 Platelet aggregation Thromboxane A2 Pain mediation, Fever induction PGE2 11. How can diet be used to control inflammation? Eicosapentaenoic acid (EPA) is released to compete with arachidonic acid (AA) for enzymatic metabolism inducing production of less inflammatory & chemotactic derivatives. In experimental animals & humans, serum PUFA levels predict the response of proinflammatory cytokines to psychologic stress; imbalance in Ω-6:Ω-3 PUFA ratio in major depression may be related to production of proinflammatory cytokines & eicosanoids. He cited a number of botanicals that are natural inhibitors of inflammatory mediators including ginkgo bilobo(platelet activating factor), Capsaicin (topical),Turmeric or Curcumin, Nettles, Feverfew and Ginger. And of course the increased use and intake of OMEGA 3’s. |
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12. How does aspirin reduce inflammation?
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it inactivates platelet cyclooxygenase for the duration of platelet lifespan (7-10 days through acetylation, causing a mild hemostatic effect
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13. Why were selective COX-2 inhibitors developed, and why did we have to remove two of the three selective COX-2 inhibitors from the U.S. market?
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COX 2 inhibitors are anti-inflammatory and able to block pain with less gastric toxicity and side effects than NSAIDS that inhibit COX1. It was discovered that these drugs increase the risk for a heart attack Because they adversely effect the ratio of thromboxane to prostacyclin and adversely effect resolvin levels. Vioxx and Betrex were pulled from the market because of this.
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1. What two different kinds of enzymes have to be produced for us to digest proteins, where do we produce these enzymes, how many different enzymes do we have to produce to digest proteins and how many different places are used for protein digestion?
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a. Proteolytic digestive enzymes – over 30
i. Gastric secretion - 1 ii. Pancreatic secretion - 6 iii. Brush border enzymes (BB) - >20 iv. Cytoplasmic – 4 b. Two types are exopeptidases and endopeptidase c. Places of use: i. Luminal digestion – in the lumen of the GI ii. Membrane digestion – by enterocytes in the BB iii. Cytoplasmic digestion – in microvillar cells d. Process: i. Proteins are broken down into oligopeptides in the lumen ii. Oligopeptides are broken down into di and tri-peptides, amino acids, and other oligo peptides by the BB using 1. Aminopeptidase – oligopeptides to tri/dipeptides and aa 2. Tripeptidase – tripeptides to dipeptides and aa 3. Dipeptidase – dipeptides to 2aa iii. Amino acids and di- and tri-peptides are transported into the cell where they are further digested |
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2. What enzyme starts protein digestion, where is this enzyme formed, how is it activated and what does this enzyme do?
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a. Pepsinogen is found in the stomach and is produced by chief cells
b. To become active it is catalyzed by HCl or pepsin (self-activation) to become pepsin (endopeptidase) c. Unfolds protein polypeptides by acid and converted to large polypeptide pieces by Pepsin (10-20% of dietary protein) d. It cleaves peptide bonds within the peptide |
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3. Where do we absorb amino acids, how much dietary protein gets
absorbed as free amino acids versus peptides? |
a. Absorbed in the stomach, small intestine (mostly), and large intestine
b. 97% from animals absorbed, 65% from plants absorbed c. Small intestine absorbs di and tri peptides d. Peptides are 2/3 of the dietary protein that gets absorbed (mentioned many times in the slides) |
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4. What enzyme produced by the brush border membrane in the gut lining is used to activate pancreatic trypsinogen?
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a. Enterokinase (enteropeptidase) converts trypsinogen to trypsin
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5. Why are all pancreatic enzymes that are used for protein digestion, except for collagenase, produced as zymogens and how do we protect the pancreas from the constant spontaneous conversion of trypsinogen to trypsin?
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a. They are secreted in inactive form so that the pancreas is not damaged by them
b. Enterokinase is outside the pancreas and the pancreas contains protease inhibitors to prevent damage from spontaneous activation of trypsinogen c. Trypsinogen also has a slow spontaneous rate of activation |
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6. How do we transport amino acids?
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a. Carrier proteins – small peptides (67%) using small peptide and H symport
b. Carrier mediated transport – amino acids (33%) using aa and Na symport c. To move across the basolateral membrane into the blood there ar at least 5 classes of aa transporters, 2 are sodium dependent (active) and 3 are sodium independent (passive) |
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7. Where are peptide transporters found, how many peptide transporters do we have, how do they work and what kind of role do they play in the absorption of dietary protein?
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a. They play a critical role in the absorption of protein digestion products and work on a proton gradient
b. PEPT1 – is in the small intestine c. PEPT2 – in the colon |
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8. What are the two major kinds of kidney stones that Americans form and how are these kinds of stones treated? Why do Americans form more stones with phosphate in them than people living in India?
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a. Calcium oxalate stones
b. Mixed calium oxalate and phosphate c. We form more because soda is high in phosphate d. Majority treated by Extra-corporeal shock wave lithotripsy (ESWL) e. 10-15% need surgery – PCNL/ureteroscopy f. Less than 1% need open surgery g. Only calcium stones can be broken up by ultrasonic shock waves |
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9. Why does magnesium citrate along with the RDA of 8 glasses of water each day decrease the incidence of kidney stones?
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a. Citrate and magnesium both inhibit crystal growth by complexing with Ca or oxalate
b. Water helps to keep the urine dilute |
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10. What kind of kidney stone did Cal Kulis form, why did he form this kind of stone and how could it have been prevented?
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a. He had a defective transport protein in the urinary tract and was unable to absorb cystine from urine
b. He formed a cystine stone |
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11. Why do carriers (heterozygotes) for cystic fibrosis have a better survival rate after exposure to the toxin produced by Cholera bacteria than non carriers and why do the homozygotes (patients with CF) die so quickly?
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a. The CFTR chloride channel has a defect in cystic fibrosis that prevents the chloride channel from opening properly
b. Cholera toxin causes the CFTR to stay open , causing diarrhea c. A heterozygous defect prevents cholera from allowing a high release of Cl into the lumen d. Those homozygous usually die early due to thickening of mucous in the lungs |
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12. How many different DNA mutations have been identified to date that cause cystic fibrosis, what is the most common mutation, what is it’s frequency, what new drug has been developed to deal with some of the genetic defects that cause CF and how does this new drug it work?
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a. A loss of phenylalanine at the position 508 is common and occurs in 70% of CF mutations (3 bp deletion)
b. There are 1546 DNA mutations that cause CF c. PTC 124 has been developed to help, and it bypasses the nonsense stop codon that is found in 2% of cases to create full length CFTR proteins instead of truncated ones |
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13. What was used to help improve Sissy Fibrosis’ survival, why was this done, what kind of problems are we now facing with this kind of therapy and what is the major cause of death for patients with cystic fibrosis?
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a. 85% of the patients have pancreatic insufficiency, so Sissy was prescribed pancreatic supplements to help her survival
b. High doses of PERT (pancreatic enzyme replacement therapy) cause severe colitis, and drug manufacturers were required to file NDA’s by 2008 c. Some extensions have been allowed by the FDA to ensure that the drugs are still on the market d. Primary cause of death in CF is cardio-respiratory |
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1. What are the two metabolic classifications that are used for amino acids?
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Glucogenic (glucose producing) and Ketogenic (ketone producing)
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2. List the 9 essential amino acids, the amount needed each day for each one ( Dr. B said we don’t need to know amount) and the function(s) of each one. Do need to know function of each.
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Leucine—1.2 grams per day. It’s a branched-chain amino acid that is used for fuel in brain and muscle.
Phenylalanine—1.1 grams per day. Aromatic amino acid that is used to form tyrosine. Competes with tryptophan for transport into the brain across the blood-brain barrier. High levels can induce a serotonin deficit (aspartame use). Also competes with tyrosine for transport across the blood-brain barrier. High levels can induce a dopamine deficit. This action of phenylalanine on movement of key amino acids into brain is thought to be the major cause of mental retardation in PKU patients. Valine—1 gram per day. Branched-chain amino acid that is used for fuel in brain and muscle. Methionine—1 gram per day. Sulfur-containing amino acid that is used to form cysteine and S-adenosylmethionine (SAM). Isoleucine—950mg per day. Branched chain amino acid that is used for fuel in brain and muscle. Lysine—800 mg per day. Positively charged (basic) amino acid. Hydroxylated lysine is a major component of collagen and is therefore needed for good wound healing. Threonine—500mg per day. Hydroxylated amino acid. Used for O-linked glycosylation and as a site in protein for hormone regulation phosphorylation. Histidine—350 mg per day. Positively charged (basic) amino acid. Used to form histamine and carnosine. Carnosine, like taurine, is an approved treatment for congestive heart failure Tryptophan—250mg per day. Aromatic amino acid. Used to form niacin, serotonin, and melatonin. |
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3. List the 5 nonessential amino acids and indicate how each one is synthesized.
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3 MADE FROM TCA CYCLE INTERMEDIATES
Aspartic acid—precursor is oxaloacetate and the enzyme is TA Asparagine--- Precursor is aspartate and the enzyme is asparagines synthetase Glutamic acid/Glutamate--- derived from alpha-ketoglutarate 2 MADE FROM GLYCOLYSIS INTERMEDIATES: Alanine—made from pyruvate by aminotransaminase (ALT) it is a reversible reaction Serine—comes from 3 phosphoglycerate (intermediate of glycolysis), it will produce cysteine and glycine |
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4. List the 7 conditionally essential amino acids and indicate how each one is synthesized. Dr. B said we need to know precursor that forms each aa but not the the enzyme
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Glutamine-glu-precursor, gln synthetase-enzyme
Glycine -serine-precursor, Proline- glu-precursor- 4 steps Arginine- glu-precursor , urea cycle Tyrosine-phenylalanine-precursor, Phe hydroxylase-enzyme Cysteine- mehtionine-precursor, 3 steps Taurine- cysteine-precursor, 4 steps |
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5. List the 18 glucogenic amino acids.
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All except for leucine and lysine. Aspartate, Asparagine, Arginine
Phenylalani Tyrosine Isoleucine Methionine, Valine, Glutamine Glutamate, Proline, Histidine Alanine, Serine Cysteine Glycine, Threonine, Tryptophan |
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6. List the 6 ketogenic amino acids and indicate which two are purely ketogenic.
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Isoleucine, Leucine, Tryptophan, Lysine, Phenylalanine, Tyrosind
Leucine and Lysine are purely ketogenic. |
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7. What tissue catabolizes most of the amino acids in blood or that come from a recent meal?
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The liver-50% of AA’s entering the liver are catabolized. It is a major site for essential AA catabolism.
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8. How many grams of protein are synthesized each day in a typical person, what is the turnover rate for different kinds of protein and why does protein breakdown and then get resynthesized on a regular basis?
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About 300 grams of protein is broken down and then resynthesized on a regular basis in humans every day.
Three reasons for protein turnover. 1. to prevent accumalation of abnormal proteins. 2. to allow rapid changes in protein concentration 3. to have a readily available source of aa’s |
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What are the two ways of getting nitrogen out of amino acids and which process produces a toxic end product. Make sure that you know what this toxic end product is and why it’s toxic.
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1. Transamination reaction-aminotransferase moves the amine to alpha ketoglutarate producing glutamateor to oxaloacetate, producing aspartate.
2. Oxidative damination-removal of the amine from glutamate producing an ammonium ion |
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10. Why is glutamate dehydrogenase such an important enzyme in amino acid metabolism? Make sure you understand where and how it it operates.
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As a reversible reaction, glutamate dehydrogenase releases ammonia in the liver and traps ammonia in extrahepatic tissues. All tissues have this enzyme but it’s especially high in the liver. See slide
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11. What are ALT and AST, why are these enzymes important, how are these enzymes used to look at liver function, what else besides ALT and AST is used to see how well the liver is working, what vitamin is required for ALT and AST activity and what happens when this vitamin is deficient. Make sure that you know how common this particular vitamin deficiency is and what the symptoms are for deficiency as well as excess (vitamin toxicity).
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Vitamin B6—the most common vitamin defieciency detected by the CDC.
Deficiency: Microcytic, hypochromic anemia, irritability, insomnia, weakness, nervousness. Toxicity: progressive numbness or tingling in feet, arms, legs, nerve malfunction (upper limit 100mg/day) |
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12. List the 4 major keto acids that are used to accept nitrogen in transamination reactions and indicate what amino acid is formed when each ketoacid is used.
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Ketoglutarate ==> Glutamate
Oxaloacetate ==> Aspartate Pyruvate ==> alanine Glyoxylate ==> Glycine |
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13. What two enzymes are used to trap ammonia?
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glutamate dehydrogenase and glutamine synthase
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14. Go through the process that the liver uses to remove nitrogen from the blood to form urea. Make sure that you understand the glucose/alanine cycle.
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see slide
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. List the 4 enzymes and the 4 intermediates in the urea cycle.
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4 enzymes
Ornithine transcarbamoylase Arginosucinate synthetase Arginosuccinase Arginase 4 intermediates citrline arginosuccinate arginene orthonine |
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15. What is the rate-limiting step in urea synthesis and how is this enzyme regulated?
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Carbamoyl Phosphate Synthetase is absolutely dependent on N-acetylglutmate
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1. What are the five major functions of nucleotides?
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1. Building blocks of nucleic acids (DNA and RNA).
2. Involved in energy storage, muscle contraction, active transport, maintenance of ion gradients. 3. Form activated intermediates in biosynthesis (e.g. UDP-glucose, S-adenosylmethionine). 4. Components of coenzymes (NAD+, NADP+, FAD, FMN, and CoA) 5. Metabolic regulators: a. Second messengers (cAMP, cGMP) b. Phosphate donors in signal transduction (ATP) c. Regulation of some enzymes via adenylation and uridylylation |
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2. What are the functions for the high-energy phosphate nucleotides and which one of these is found in the highest level in cells?
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Precursors to DNA & RNA, carriers of energy via phosphoryl group transfer, serve as recognition units, cyclic nucleotides are signal molecules and regulators of cellular metabolism and reproduction.
ATP is central to energy metabolism GTP drives protein synthesis CTP drive lipid synthesis UTP drives carbohydrate metabolism Energy metabolism (ATP) found in the highest levels in cells |
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3. What is adenosine, how is it formed, what is it formed from, what does it do, how does it alter cellular metabolism and what plant chemical blocks the action of adenosine in the human body?
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Adenosine is formed by the breakdown of ATP—formed in all cells
It is secreted (as hormone) into bloodstream where it binds to receptors on another cell surface and initiates changes in that target cell Hormonal action of adenosine- Induces vasodialation Induces smooth muscle contraction Release of neurotransmitters Induces sleepiness (countered by caffeine Blocked by plant chemical Caffeine Binds to the adenosine receptor and blocks them Binds to phosphodiesterase and prevents it from converting cAMP to ATP Caffeine was originally produced to kill insects |
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4. Where do nucleotides come from and how do we process them? Make sure that you know the names for the 4 enzymes that we use to process nucleotides coming from food or inside cells.
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Sources of nucleotides from DNA and RNA include diet, cellular turnover, de novo synthesis and salvage (from breakdown). They are broken down in this process illustrated in diagram, which includes the enzymes needed as well.
deoxyribonuclease, ribonuclease, 5-nucleotidase and nucleotidase are 4 enzymes needed!!! |
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5. How do we synthesize nucleotides? Make sure that you know the end products for each pathway.
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Conversion of both involve nucleside diphosphate kinase.end products for purines are ATP and GTP, for pyridimines it is UTP
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6. Name the first purine nucleotide and pyrimidine nucleotide formed during the de novo synthesis of nucleotides.
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The first purine nucleotide formed is IMP (inosine monophosphate) but it’s only used as a precursor for Adenine/Guanine
The first pyrimidine nucleotide formed is OMP (orotidine 5’-monophosphate) |
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7. What is the rate-limiting step for purine nucleotide synthesis and how is the activity of this enzyme controlled?
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The rate-limiting enzyme is Amidophosphoribosyl
transferase. AMP, ADP, and ATP negatively inhibit PRPP formation activates the enzyme |
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8. What is the rate-limiting step for pyrimidine nucleotide synthesis and how is the activity of this enzyme controlled?
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The rate-limiting enzyme is Carbomoyl phosphate synthetase
The enzyme is inhibited by UTP and CTP and activated by ATP |
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9. What are the two end products of pyrimidine base degradation, which one of these is an important compound and why is it important?
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Pyrimidine nucleotides are degraded to beta-alanine (useful metabolite -beta alanine will react w/ histidine to form carnosine) and beta amnioisobutyric acid.
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10. What is the end product of purine base degradation and why is this compound specific to primates?
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Purine nucleotides are degraded to Uric Acid (toxic waste producte). In primates, purine catabolism ends with uric acid and it is excreted. Primates have the gene for urate oxidase but it’s a non-functional gene (mutated early in primate evolution).
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11. What is PRPP, what enzyme forms it, where does the substrate for this enzyme come from and what is PRPP used for?
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PRPP is an activated form of ribose. Ribose-5- Phosphate. It comes from the pentose phosphate pathway. R5P pyrophosphokinase is the enzyme used in formation of PRPP. PRPP is used for both nucleotide synthesis and salvage
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12. What are the salvage pathways for the purines and the pyrimidines and why are these pathways important?
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This same process (react a base with PRPP) is also used for pyrimidine salvage. Salvage pathways are used to recover bases and nucleosides that are formed during degradation of RNA and DNA. This is important in some organs because some tissues cannot undergo de novo synthesis.
(incomplete) |
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13. What is gout and how is it treated?
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Excess uric acid causes gout (results form overactive denovo synthesis pathway). This leads to deposit of uric acid in the joints. The treatment of an acute attack of gouty arthritis involves measures and medications that reduce inflammation. Preventing future acute gout attacks is equally as important as treating the acute arthritis. Prevention of acute gout involves maintaining adequate fluid intake, weight reduction, dietary changes, reduction in alcohol consumption, and medications to lower the uric acid level in the blood (reduce hyperuricemia).
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14. What other disorders of purine metabolism besides gout occur in humans and what causes these other disorders?
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Lesh-Nyan syndrome is caused by a genetic deficiency of HGPRT. Severe Combined Immunodeficiency (SCIDs) is caused by a deficiency of B lymphocytes, mutations effect the active site of adenosine deaminase. Then DATP (x50) inhibits ribonucleotide reductase, key enzyme in the synthesis of dNDPs => dNTPs for DNA synthesis
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. List the two nucleotides that are used to form deoxythymidine monophosphate and list the two enzymes that are needed to convert dUTP to dTMP.
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CDP and UDP are 2 nucleotides used to form deoxythymidine monophosphate
dUTPase and thymidylate synthase are 2 enzymes used in process |
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15. What are aminopterin and methotrexate, what do they do and what are they used for
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These are competitive inhibitors of dihydrofolate reductase (DHFR) and used in cancer tx (see slide)
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16. What is 5-flurouracil, what does it do and what is it used for?
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It is a chemotherapy agent used against cancer as a thymidylate synthase inhibitor
Knocks out DNA synthesis---very specific |
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17. Name the enzyme needed to form deoxyribonucleotides and indicate how the activity of this enzyme is regulated
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Ribonucleotide reductase is needed to form deoxyribonucleotides. + regulation by ATP and – regulation by dATP, dGTP, TTP and dCTP
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1. Understand the definitions of endocrine, paracine, autocrine and intracrine. Be able to apply the terms to a biological example. Synaptic neurotransmission is a specialized form of which type of signaling?
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Endocrine -glands synthesize & secrete hormones into the bloodstream
hormones have physiological affects on distal target tissues Paracrine cells synthesize & secrete a substance into the extracellular space to affect targets on nearby cells Autocrine a cell synthesizes & secretes a substance that affects targets on the same cell Intracrine a cell synthesizes a substance that affects targets in the same cell (usually pertains the hydrophobic signaling molecules) One signaling molecule can act at multiple levels simultaneously Example: Insulin release from pancreatic β islet cells Insulin is secreted in response to high blood glucose Endocrine Insulin enters the bloodstream and travels to distal sites to: increase cellular glucose uptake stimulate cellular glycolysis promote storage of nutrients (glycogen synthesis) Paracrine Insulin inhibits the secretion of glucagon from α islet cells Autocrine Insulin inhibits release of more insulin from β islet cells Synaptic neurotransmission is a specialized form of which type of signaling? Synaptic neurotransmission is a specialized form of ligand-gated ion channel receptors. |
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2. Most signals are transduced by cell surface receptors, however some signaling molecules use intracellular receptors. What is the defining characteristic of signaling molecules that bind to intracellular receptors?
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Intracellular receptors
Receptors in cytoplasm or nucleus for hydrophobic signaling molecules(these bind to intracellular receptors) steroid hormones derivatives of vitamin D3 retinoic acid thyroid hormone alter gene transcription activated intracellular receptors are transcription factors |
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3. Understand the terms ligand, agonist and antagonist. What is the difference between a competitive and a non-competitive antagonist?
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Ligand: any molecule that binds to a receptor protein (usually to plasma membrane receptors)
Agonist: A ligand that activates signal transduction Test question: Antagonist: A ligand that prevents signal transduction Competitive: bind at the agonist binding site Affinity Matters Non-competitive: bind at other sites on the receptor Affinity Does NOT matter (used more in pharmacology) |
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4. Understand what is meant by a receptor subtype.
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one endogenous ligand can bind to several entirely different receptor proteins that are products of different genes
receptor subtypes generate an extra level of specifity they can be expressed differentially in different tissues they can couple to different effectors in many cases the site of agonist release also contributes to specificity synthetic ligands are usually designed to be receptor subtype specific |
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What are the differences between nicotinic and muscarinic receptors?
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Nicotinic receptors are gated ion channel receptors on skeletal muscle cells
Muscarinic receptors are G protein receptors on Heart Muscle Cells (parasympathetic) |
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What effects do nicotinic and muscarinic receptors mediate in skeletal and cardiac muscle, respectively?
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Nicotinic receptors stimulate contraction in skeletal muscle
Muscarinic receptors stimulate hyperpolarization---deter contraction |
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What are nicotinic and muscarinic receptors' endogenous agonists?
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Acetylcholine
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How do the nicotinic and muscarinic receptor proteins differ?
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Nicotinic = gated ion channel receptors
Muscarinic= G protein receptors |
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5. Understand the definitions of KD and EC50.
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KD: Is the dissociation constant or the concentration of agonist where 50% of the binding sites are occupied
Affinity is inversely related to KD. In practice, affinity is stated in terms of KD EC50: is the half-maximal effective concentration (measured from functional responses-dose response curve) Generally considerably lower [agonist] than the KD If both are determined in the same tissue, with the same agonist, which will usually have the lower concentration value? EC 50 What is the physiological significance of this difference? The effect will occur before the Kd is reached, and therefore does not give a lot of information about what dosage will work or be safe The EC50 will tell you more about concentration and physiological effect What is the relationship of KD and affinity? Affinity is inversely related to KD. In practice, affinity is stated in terms of KD Why is it important to know the affinity of a competitive antagonist? If the affinity of a competitive agonist were extremely high, a small amount of the competitive agonist would be necessary to interfere with endogenous ligand binding. Conversely, if the affinity of the competitor were low, it would take a much higher concentration of the competitor to effectively compete for the binding site because the endogenous ligand will be binding instead. |
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6. What is the therapeutic index, and what happens if it is too low?
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LD50/ED50
LD50 = lethal dose: the concentration of agonist that kills half of all animals ED50 is equivalent to EC50 If it is too low then the effective dose will be close to the lethal dose and it will be difficult to administer the right amount to be effective without causing death |
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. The binding of agonist to receptor initiates the first step in signal transduction – what is this step?
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Ligand binding causes a change in receptor conformation
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7. What are three mechanisms for terminating signal transduction?
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Decrease agonist availability
effectiveness depends on the size of the compartment plays a major role in synaptic signaling agonist re-uptake (serotonin, dopamine) agonist degradation (acetylcholinesterase) Receptor desensitization – receptor stops signaling in the presence of agonist intrinsic (AMPA-type glutamate receptors, nicotinic ACh receptors) secondary to receptor phosphorylation (can be a form of negative feedback) Internalization of ligand / receptor complex unliganded receptor can be returned to the cell surface ligand and receptor can be targeted to the lysosome for degradation results in fewer cell surface receptors ==> receptor down-regulation |
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Which mechanism of terminating signal transduction is used to terminate signaling primarily in small compartments?
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Decrease agonist availability (remember the concentration has to be higher to have an effect
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Name two examples of terminating agonist availability to terminate signal transduction in small compartments
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Agonist reuptake (serotonin, dopamine)
Agonist degradation (acetylcholinesterase) |
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If the receptor is internalized it has two possible fates – what are these?
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unliganded receptor can be returned to the cell surface
iigand and receptor can be targeted to the lysosome for degradation results in fewer cell surface receptors ==> receptor down-regulation |
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What is receptor down-regulation?
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Fewer cell surface receptors available such as in example of ligand and receptor being targeted for degradation
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8. Ligand-gated ion channel receptors mediate very fast signal transduction. Why are they so fast?
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very fast - only one molecule is involved, with no enzymatic reactions
After the receptor is opened, what are the intracellular transduction steps that follow? When the ligand-gated ion channel opens: Cation-selective receptors (Na+ and / or Ca2+ influx) are excitatory gated by excitatory neurotransmitters (glutamate, acetlycholine, serotonin, ATP) Anion-selective receptors (Cl- influx) are inhibitory gated by inhibitory neurotransmitters (GABA, glycine) A change in membrane potential -effects the neuron’s probability of firing an action potential -effects activation of voltage-gated Ca2+ channels Ca2+ is an important second messenger effects activation of Ca2+ binding regulatory proteins If an increase in cytosolic calcium levels is the last of these steps, be able to list at least three Ca2+-sensitive effector proteins, and what physiological functions they mediate. synaptotagmin in release of synaptic vesicles troponin-C in contraction of striated muscle calmodulin & CaM kinase II in protein phosphorylatio and alterations in gene expression |
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9. What is typical resting cytosolic Ca2+ concentration?
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Cytosolic [Ca2+] = 10-7 M
greater extracellularly |
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Extracellular Ca2+ concentration?
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Extracellular [Ca2+] = 10-3 M
greater extracellularly |
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The concentration at which Ca2+-sensitive effector proteins are activated?
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Cytosolic [Ca2+] = 10-6M is sufficient to maximally activate Ca2+ sensitive proteins
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What two proteins in the plasma membrane maintain the Ca2+ gradient?
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Sodium (Na2+) calcium exchanger
Calcium ATPase |
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Release from intracellular organelles can also elevate cytosolic Ca2+ levels. Name an organelle that can release Ca2+.
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Endoplasmic reticulum
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How is the release of calcium from the ER triggered?
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The cleavage of the Gqα subunit into Inositol 1,4,5-triphosphate which will openi IP3 gated calcium release channels
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10. The endogenous agonists for ligand-gated ion channel receptors are classed as excitatory or inhibitory neurotransmitters based on what property of the receptor?
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The receptor will be made of subunits with different properties
GluR1,3,& 4 are Q which means high glutamate affinity GluR2 is R which means it has arginine in it, a positive cation. So it will not react with calcium. The more of this subunit you have in the receptor the less likely it will react to glutamine and/or calcium Different receptors will differ with regard to: Calcium permeability Single-channel conductance Desensitization properties |
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Protein structure determines protein function – what is the moleculer basis for this property?
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When a ligand binds to a protein it will make a conformational (structural) change that will produce an effect of either activating or inhibiting another process
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11. Ligand-gated ion channel receptor signaling is often terminated by desensitization. What is meant by desensitization?
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Receptor desensitization – receptor stops signaling in the presence of agonist
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How does an AMPA-type glutamate receptor desensitize?
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See powerpoint-she spent some time on the above slide when discussing desensitization…
A ligand-gated ion channel can close when agonist is still bound (desensitization) |
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. For ligand-gated ion channel receptors the receptor and the ion channel are part of the same molecule. However, some ion channels are opened (or gated) by separate molecules. Name a specific example of this latter case - be able to name the separate molecule, explain how the signal is transduced to the ion channel and what the final physiological effect is.
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The muscarinic acetylcholine receptor in the heart is an example of this. It has a separate Potassium channel that is blocked
When acetylcholine binds, the Giα subunit will bind and GDP will disassociate to be replaced with GTP, then the Gβgamma subunit will disassociate as well and bind to the potassium channel which will open the channel and release the potassium from the cell, slowing down the heart rate |
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14. Name two major groups of enzyme-linked receptors.
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Receptor tyrosine kinases- epidermal growth factor (EGF), platelet derived growth factor (PDGF), insulin
Receptor serine/threonine kinases- transforming growth factor-β (TGFβ), bonemorphogenetic proteins (BMPs) Both are monomers that must dimerize to work |
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To which group of enzyme-linked receptors does the insulin receptor belong?
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Dr T likes this one
Receptor tyrosine kinases |
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For enzyme-linked receptors, what is the major function of the extracellular domain?
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Extracellular—where ligand binds
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What is the major function of the intracellular domain of enzyme-linked receptors?
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Intracellular--- where the kinase is activated
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Understand how agonist binding leads to the recruitment of a signaling complex.
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Tyrosine Kinase
Ligand binding causes receptor dimerization Dimerizaed receptors transphosphorylate on tyrosine residues Phosphorylated tyrosines act as recognition and anchoring sites to recruit other signaling proteins, which in turn are phosphorylated on tyrosine residues by the activated receptor Kinase cascades eventually phosphorylate effector molecules to alter their activity or cause changes in gene expression Serine/Threonine kinases Ligand binding causes receptor dimerization Dimerized receptors transphosphorylate on Ser/Thr residues Phosphorylated receptors can recruit and phosphorylate SMAD proteins This phosphorylation allows SMADs to unfold, dimerize, and translocate to the nucleus, where they modulate gene expression |
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In general terms, what are the molecular effects at the end of the signaling cascade? How is receptor signaling terminated?
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Signaling is terminated by receptor internalization, with recycling to the membrane
SH2 and PTB domains bind to the specific P-Tyr SH3 domains bind to proline rich domains that characterize certain signaling proteins |
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What is the major difference between the class of enzyme-linked receptors and cytokine receptors?
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They are both transmembrane receptor proteins, but cytokine receptors lack intrinsic catalytic activity
They will have protein binding domains instead |
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What characteristics of their agonists do both classes of receptors (enzyme-linked and cytokine receptors) share?
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They both use large secreted proteins as agonists---paracrine
Although enzyme---endocrine Cytokine---autocrine |
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What is an adaptor molecule?
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Adaptor molecule = PSD-95
It is accessory to main proteins in signal transduction. They lack any intrinsic enzymatic activity but instead mediate specific protein-protein interactions that drive the formation of protein complexes |
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Know what SH2, SH3, PTB and PH domains bind to.
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SH2 and PTB (phosphotyrosine binding proteins) bind to the phosphotylated tyrosines
SH3: will bind to proline rich domains that are characteristic of certain signaling molecules PH (Pleckstrin homology) domains bind to phosphatidylinositol derivatives |
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. Cytokine receptors are important for which major aspects of human physiology
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Hematopoiesis
Immune and inflammatory response (include interleukins and interferons) |
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For cytokine receptors, understand how agonist binding leads to the recruitment of a signaling complex.
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When a cytokine binds, the JAK proteins are activated and begin to phosphorylate one another
This recruits the STATs already in the cell to come phosphorylate themselves |
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What type of proteins are JAKs?
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Non-receptor (soluble) Tyrosine kinases---janus kinases
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What type of proteins are STATs? This answer from wikepedia….in notes??
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Signal Transducers and Activator of Transcription (STAT, also, called signal transduction and transcription) proteins regulate many aspects of cell growth, survival and differentiation. The transcription factors of this family are activated by the Janus Kinase JAK
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What is the result of STAT phosphorylation (list all the steps)?
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STAT proteins bind to the activated receptors and are themselves phosphorylated
Phosphorylated STATs dissociate from the receptor and can now dimerize, translocate to the nucleus, and act as transcription factors. |
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. G-protein coupled receptors are a large and diverse family, but they all share the same membrane topology – what is this topology?
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Heterotrimeric G-proteins for signal transduction
Look like wound up strings with clumps in the membrane extracellular loops form the ligand-binding domain intracellular loops 2 and 3 bind the G-protein α subunit |
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Understand the how a G-protein works. What is the function of GDP binding?
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G-protein will be bound to the –and GDP which gives it a high affinity for ---
When the receptor is activated it will change conformation and increase affinity for the Gα subunit The Gα will bind to the activated receptor The binding will induce a change in the Gα protein and GDP will disassociate GTP is at a high concentration in the cytosol and so will bind to the Gα This decreases the affinity of Gα for the Gβγ and will dissociate leaving the βγ attached to the activated receptor Gα and GTP will then bind the inactive effector molecule (adenylate cyclase or phospholipase C) Once it binds at the effector molecule an internal clock is set, and the Gα will continue to interact with other molecules until it is hydrolyzed back to GDP so that it will reassociate with the Gβγ and go back into its resting state G-proteins are classed by their α subunits. Contain the GDP/GTP binding site, and intrinsic GTPase activity attached to the inner leaflet of the plasma membrane by a lipid anchor Understand the transduction pathways for αs,αi, and αq. Be able to identify the effector molecule, and the second messengers involved for each. αs increases adenylate cyclase activity ==> increases cAMP levels (second messenger) αi decreases adenylate cyclase activity ==> decreases cAMP levels (second messenger) αq increases phospholipase C activity ==> increases IP3 levels, increases DAG levels (second messenger) |
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22 . After G-protein α and βγ subunits dissociate the βγ subunits can serve three important functions – what are they?
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βγ subunits can also have signaling effects:
they can activate K+ channels or inhibit Voltage-Gated Ca2+ Channels βγ subunit composition can also effect which receptor the G-protein interacts with |
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What enzyme synthesizes cAMP?
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Adenylate cyclase
From which substrate? ATP What enzyme family breaks down cAMP? Phosphodiesterase (PDE’s) How does cAMP activate Protein Kinase A (PKA)? Binds to the regulatory subunits of protein kinase A and causes the regulatory subunits to dissociate from the catalytic subunits leaving the ATP and substrate binding sites on the catalytic subunits exposed How does activated PKA alter cellular function? It phosphorylates target proteins which will alter gene expression |
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24. What is AKAP, and what does it do?
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AKAP (A Kinase Anchoring Protein)
Is a multivalent adaptor protein that can localize PKA: near target proteins (to increase specificity) near adenylyl cyclase (to increase sensitivity) near phosphodiesterases (to limit the duration of the signal How does this effect signal transduction? Can limit the duration of the signal |
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25. Understand the mechanism of action for cholera toxin and pertussis toxin.
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Both will bind to the cell surface receptors and the enzymatic subunit is internalized ( ADP-ribosyl transferase)
Will turn on the Gα subunit (they differ) but they are not turned off so it just keeps acting on the effector molecule or they completely inhibit the G-protein What molecules do they target? Cholera targets: αs Pertussis targets: αi and αo What do the toxins do to their targets, and what is the effect on signal transduction? Cholera toxin binds to cell surface receptors enzymatic subunit ( an ADP-ribosyl transferase) is internalized toxin transfers an ADP-ribose from NAD to Arg210 on αS this inhibits the GTPase activity of αS which enhances activation of adenylate cyclase in intestinal epithelial cells results in the increased secretion of H2O-diarrhea Pertussis toxin also an ADP-ribosyl transferase toxin transfers an ADP-ribose to a Cys near the COOH term of αI & αO this inhibits interaction with G-protein coupled receptors which results in no signal transduction |
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Phospholipase C cleaves phosphatidylinositol-4, 5-bisphosphate into two molecules, both of which are second messengers. Name the two molecules and trace out the steps in their signal transduction.
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Inositol 1,4,5-triphosphate (IP3)
PI 4,5,-biphosphate Ligand binds to a G-protein coupled receptor, which activates Gαq, which in turn activates phospholipase C Phospholipase C hydrolyzes phosphoinositide 4,5-biphosphate (PIP2, which is inserted in the membrane) into inositol 1,4,5-triphosphate (IP3, which diffuses away into the cytoplasm), and 1,2-diacylglycerol (DAG, which remains in the membrane) Do they remain attached to the membrane? The PI 4,5,-biphosphate does |
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What are the normal steps to turning off GPCR signal transduction after the signal is gone?
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Turning off the response when the signal is gone
Hormone dissociating from the receptor is determined by hormone concentration and Kd for receptor G-protein hydrolysis of GTP-this can be sped by GTPase activator proteins (GAPs) Phosphodiesterase degradation of cAMP Dephosphorylation of target proteins by phosphatases |
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Understand the process by which GPCR signal transduction is terminated in the continued presence of agonist.
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Turning off the response in the continued presence of signal
Desensitization Internalization recycling of the receptor to the cell surface receptor degradation in the lysosome |
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What are the major hormones produced by the hypothalamus
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TRH, ADH, and oxytocin
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What are the major hormones produced by the anterior pituitary
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ACTH, FSH, LH, TSH, PR, and GH
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What are the major hormones produced by the posterior pituitary
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Oxytocin and vasopressin (released here)
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What are the major hormones produced by the thyroid gland
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Thyroxin, T3 and T4
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What are the major hormones produced by the heart
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ANF
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What are the major hormones produced by the adipose tissue
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leptin, adiponectin, resistin, TNF-alpha
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2. Understand what a negative feedback loop is and how it works.
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The final hormone inhibits the earlier steps in the cascade and regulates the amount of final hormone. Ex. Cortisol decreases transcription of gene for ACTH.
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3. Most peptide hormones are encoded by a single gene – name three exceptions
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TSH, LH and FSH are exceptions.
How are the α chains of these three hormones related? these 3 share a common α chain (which is encoded by one gene), How are the β chains related? have unique β chains (which are encoded by three separate genes). What is the physiological significance of having two subunits? |
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4. Many peptide hormones are processed from longer precursors. What determines where the precursors will be cut?
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Cleavage most frequently occurs between two basic amino acids
– ArgLys, ArgArg, LysLys, LysArg, but adjacent amino acids contribute to the specificity of the cleavage signal.) This may be necessary to: achieve proper protein folding (insulin) ensure constituent hormones are expressed in the correct ratios (vasopressin, oxytocin) increase hormone repertoire In what subcellular compartment does the cleavage occur? Cleavage occurs in the ER and golgi. What happens to the rest of the precursor after cleavage? It is often times co-secreted as in the case of Insulin and C-peptide Keeps ratios in check In the case of vasopressing or oxytocin, the rest is used as a carrier protein (neurophysin I or II) What controls the selective proteolysis of proopiomelanocortin? The mRNA in POMC is cleaved differently in different cell types aka it is tissue specific |
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5. β-endorphin and Met-enkephalin are involved in what physiological process?
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Both are endogenous opioid peptide neurotransmitters that have analgesic effects in the body to numb or dull pains.
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6. In melanocytes, which physiological process is controlled by the melanocortin-1
receptor? Mutations in MC1R that prevent it from signaling cause what phenotype in humans? What are the clinical ramifications of this phenotype? |
the melanocortin 1 receptor on melanocytes MC1R (a GPCR) controls which pigment is produced. Autosomal recessive mutations in MC1R produce red hair and fair skin in humans. These mutations cause an increased rate of skin cancer and reduced tolerance to pain
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What are the five major classes of peptide hormone membrane receptors?
For each class understand how receptor activation couples to second messenger systems, how second messengers alter the location or activity of proteins, and how second messengers are cleared from the cytosol. Understand how PKA, PKB, and PKC are activated. |
PKA is activated by cAMP, which will bind to the reg subunits of PKA and cause reg subunits to dissociate from catalytic subunits. Then the ATP and substrate binding sites are now exposed and go into the nucleus to change gene expression
PKB recruited by PIP3 as well as PKD. PKD will then phophyorylate PKB which will activate phophorylate target proteins PKC involved in controlling the function of other proteins through the phophorylation of hydroxyl groups of serine and threonine amino acid residues on these proteins. PKC enzymes in turn are activated by signals such as increases in the concentration of diaglycerol Hence PKC enzymes play important roles in several signal transduction cascades. |
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What controls the synthesis of PNMT?
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Coritsol increases the transciption of PNMT, the enzyme that converts Norepinephrine to
Epinephrine |
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What controls the release of epinephrine?
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Epinephrine is released by a signal from the CNS, which will release ACh. Epinephrine is stored in vesicles in the adrenal medulla chrommafin cells for times of high stress.
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What are the ligands for ErbB receptors?
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Erb1,2,3,and 4.
Erb 2 is the most potent signaling; the rest will produce weak signals Erbs must dimerize |
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ErbB signaling is important for what physiological processes?
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Important for the development of the nervous system. Promote proliferation, differentiation, and migration.
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What is the effect on signaling of including an ErbB2 subunit in a receptor dimer?
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Increases cell proliferation
Increases cell migration Resists apoptosis Too much ErbB will promote tumor growth |
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What is Herceptin? What disease is it used to treat?
How, specifically, does it interfere with ErbB signaling? |
Monoclonal antibodies directed against the extracellular domain of ErbB2 can block receptor dimerization and signaling (from powerpoint slide 8 in peptide hormones 2)
Used to treat breast cancer. Decreases rate of mitosis & tumor spread. |
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β-cells secrete insulin in response to high blood glucose. How do β-cells sense high blood glucose, and how is that coupled to insulin release.
What is the role of GLUT2? The ATP-dependent K+ channel? Voltage-gated Ca2+ channels? |
Insulin secretion from β islet cells
Glucose is transported into the cell by the GLUT2 transporter and immediately enters the glycolytic pathway High blood glucose results in higher rates of glycolysis and ↑ [ATP] ATP binds intracellularly to an ATP-gated K+ channel, which closes the channel This depolarizes the cell, which opens voltage-gated Ca2+ channels Increased intracellular Ca2+ causes insulin release Glucose is transported into the cell by the GLUT2 transporter ATP binds intracellularly to an ATP-gated K+ channel, which closes the channel This depolarizes the cell, which opens voltage-gated Ca2+ channels Increased intracellular Ca2+ causes insulin release |
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What are sulfonylureas, and what is their mechanism of action?
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Sulfonylureas bind to the SUR1 subunits of the ATP-gated K+ channel and
close the channel ==> increased insulin release |
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Understand how insulin receptor activation leads to:
Increased glucose uptake Increased rate of glycolysis Increased glycogen synthesis |
Increased glucose: Phospho-IRS recruites PI 3-kinase, which is phosphorylated
Activated PI 3-kinase binds PIP2 on the membrane and converts it to PIP3 PIP3 recruits PDK1 and Protein kinase B (PKB or Akt) to the membrane Once they have both bound PDK1 phosphorylates PKB PKB is a serine/threonine kinase Activated PKB dissociates from the PIP3 to phosphorylate target proteins One target is the glucose transporter GLUT4 in vesicles Phosphorylation of GLUT4 promotes insertion into the plasma membrane Increased rate of glycolysis: Fructose 2,6-P2 is a positive allosteric modulator of 6-phosphofructo-1-kinase ==> more fructose 2,6-P2 will stimulate gylcolysis Glucagon activates Gαs and PKA, resulting in the phosphorylation of EnzymeX Phosphorylated EnzymeX acts as a phosphatase and converts fructose 2,6-P2 to fructose 6-P ==> less fructose 2,6-P2 slows glycolysis Insulin lowers cAMP levels, and activates a phosphatase that dephosphorylates EnzymeX Dephospo-EnzymeX acts as a kinase and convert fructose 6-P to fructose 2,6-P2 ==> more fructose 2,6-P2 stimulates gylcolysis Increased glycogen synthesis: Insulin binding leads to PKB activation (as detailed above) PKB phosphorylates Glycogen Synthase Kinase 3 (GSK3), which inactivates it (active GSK3 would phosphorylate glycogen synthase, which lowers its activity) Inactive GSK3 ==> dephospho glycogen synthase, which is more active ==> more glycogen synthesis |
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What is GLP-1 and where is it secreted?
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Glucagon-like peptide–1 is an incretin peptide
secreted in upper gut |
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What four effects does GLP-1 have on pancreatic β-cells?
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Increase insulin biosynthesis
Increase glucose-dependent insulin release Increase β-cell proliferation Decrease β-cell apoptosis |
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How is GLP-1 degraded?
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GLP-1 is rapidly degraded by DPP-IV
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What is the pharmacological significance of GLP-1 degredation pathway (by DPP-IV)?
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GLP-1 is rapidly degraded by DPP-IV
incretin mimetics or DPP-IV inhibitors are used to treat type 2 diabetes |
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What is PPARγ? What roles does it play in adipocytes? Why is this of therapeutic interest?
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A transcription factor activated by fat cells that:
increases: Leptin Activates neurons in hypothalamus Results in decreased feeding secretion of TRH and CRH Changes metabolic rate TNF-α, REsistin , and Free fatty acids (These 3 compounds will INCREASE INSULIN RESISTANCE_ Decreases Adiponectin: keeps the body insulin sensitive Overall Adipocyte differentiation Adipocyte apoptosis Regulate insulin sensitivity Increasing triglyceride clearance Agonistic Controlling of PPAR can increase insulin sensitivity on adiopcytes and be therapeutic in treating insulin resistance. |
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What is somatostatin? Where is it released, and what is its physiological function?
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A peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G-protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones. Released by Delta cells in pancreatic islet and also secreted in stomach and small intestine.
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17. Although pituitary adenomas rarely progress to malignancy they can cause serious symptoms. Name two reasons why.
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They often cause pressure on parts of the pituitary gland and lead to excessive secretion of a hormone.
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18. Understand the cellular pathway for producing thyroid hormone. What does thyroid peroxidase do?
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Iodide is taken up at the basal membrane of the follicular cell against both electrical and concentration gradients
==> requires energy Thyroglobulin is synthesized and secreted into the lumen It has ~140 tyrosine residues (not unusually high concentration) Thyroid peroxidase (TPO) on the cell’s apical membrane: 1. oxidizes iodide 2. catalyzes iodination of tyrosine residues 3. couples MIT and DIT coupling is both intra- and intermolecular (only ~3 residues per molecule) Colloid droplet endocytosed Droplet fuses with lysosomes thyroglobulin hydrolized to constituent amino acids T4 and T3 are secreted |
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19. What is the relationship between T4 and T3? (Relative amounts, biological activity, etc.)
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Both T3 and T4 are secreted from thyroid follicular cells (~9% T3, ~90% T4)
< 0.3% of T3 free in the blood T4 can be deiodinated in periphery to become T3, which is the active form |
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What are the major functions of thyroid hormone?
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Functions of thyroid hormone
Crucial for growth and development critical period for CNS development (mid-gestation → ~ 2yrs) perinatal lung maturation bone maturation Controls Basal Metabolic Rate TEST******Stimulates all metabolic pathways, both anabolic & catabolic****** increases levels & activity of Na+/ K+ ATPase may increase the # and size of mitochondria increases sensitivity to epinephrine increases levels of β-adrenergic receptor increases efficacy of downstream coupling ==> increased heart rate, liver gluconeogenesis, glycogenolysis |
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How is thyroid hormone transported in the blood?
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By plasma carrier proteins
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How is thyroid hormone deactivated?
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T3 and T4 are deactivated by progressive deiodination
==> 80% of circulating T3 is produced by peripheral deiodination The thyroid hormone receptor is a nuclear steroid hormone receptor ==> the liganded receptor acts as a transcription factor |
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Know the symptoms and molecular causes of the Diabetes Insipidus
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Symptoms: Polyuria, polydispia
Blood may have high osmolality, but blood glucose is normal Central: Caused by hypothalamic damage Can be treated by desmopressin (a long acting analogue of vasopressin) Nephrogenic – Kidneys are insensitive to vasopressin |
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Know the symptoms and molecular causes of the Diabetes Mellitus
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Defined by high glucose levels
Symptoms: Poluria, polydispia, wt loss, fatigue, blurred vision, thrush. Most common cause of blindness in working age End-stage renal failure requiring dialysis Non- traumatic amputation Microvascular changes & accelerated atherosclerosis – important in the etiology of the heart attack & stroke. Type 1 – Beta cell destruction- usually complete lack of insulin Autoimmune or idiopathic Type 2 – Combination of insulin resistance and deficiency. Resistance due to mutations in the insulin receptors are rare Have complex phenotypes – insulin is a major growth factor for fetus For late set, defects found in: IRS tyrosine phosphorylation PI3 Kinase activation |
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Know the symptoms and molecular causes of acromegaly
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Excessive secretion of GH.
After epiphyses have fused results in ACROMEG (rare) Symptoms: Carpal tunnel syndrome, arthritis, excessive sweating. Usually caused by a pituitary tumor |
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Know the symptoms and molecular causes of Endemic cretinism
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Due to dietary iodine defiency brain damage severe and irreversible. Prenatal lung maturation, bone maturation
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Know the symptoms and molecular causes of goiter
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By iodine deficiency, which results in thyroid hypertrophy due to excess TSH secretion.
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Know the symptoms and molecular cause of hyperthyroidism
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Heat intolerance, weight loss, and fatigue
May be caused by Grave’s Disease(80%) Autoimmune :Ab that ACTIVATE TSH receptor |
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Know the symptoms and molecular cause of hypothyroidism
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Intolerance to cold, weight gains, lethargy
Hashimoto’s Disease (~90%) autoimmune: caused by Ab to TPO or thyroglobulin, which can eventually destroy the gland |
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Symptoms and causes of Multiple endocrine neoplasias (MEN)
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Autosomal dominant
Presents as hyperparathyroidism in most carriers, usually by age 40 Men – 1 Loss of function of mutation in menin, a tumor suppressor gene Tumors in parathyroids = 90& (can be reason for hyperparathy.) Pituitary = 60% Pancreas = 70% usually very low to progress Men – 2a Loss of fun. Mutation in ret, a tumor suppressor gene. Medullary thyroid cancer – greater than 90% Tumors in Parathryoids Both treated by surgical removal of glands/tumors |
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What are the major hormones involved in calcium homeostasis?
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Vitamin D3 (calcitrol)
PTH Calcitonin |
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What are the important intracellular roles of calcium?
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Excitation – contraction coupling
Secretion And it acts as a second messenger Understand the process by which calcium is transported from the intestinal lumen into the bloodstream. |
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What three hormone systems control fluid balance?
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Vasopressin or ADH
Renin/Angiotensin/Aldosterone system Atrial Natriuretic Factor |
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Understand how each works individually, and how they interact...
Vasopressin |
Secreted from the posterior pituitary in response to:
high osmolarity (osmoreceptors in hypothalamus) low blood pressure (baroreceptors in left atrium and carotid sinus) V2R insert aquaporin 2 into the apical surface of cells in the distal tubule of the kidney ==> increased reabsorption of water V1R vasoconstriction (GPCR Gαq) |
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Understand how each works individually, and how they interact.
Renin / Angiotensin system |
Renin is secreted from the juxtaglomerular cells of the kidney in response to low blood pressure and low [Na+]
Renin cleaves angiotensinogen (produced in the liver) resulting in angiotensin I (a decapaptide, that is NOT biologically active) Angiotensin Converting Enzyme (on endothelial cells) then cleaves angiotensin I and forms angiotensin II (an octapeptide) Aminopeptidase can then cleave this to form angiotensin III |
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Understand how each works individually, and how they interact.
Actions of Angiotensin II |
Stimulates synthesis of aldosterone in the adrenal glomerulosa cell
Causes a direct increase in renal tubular Na+ and water reabsorption Causes direct vasoconstriction Stimulates the sympathetic nervous system norepinephrine release Acts in the CNS to stimulate thirst |
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Aldosterone
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Aldosterone is synthesized from progesterone in the zona glomerulosa
The aldosterone, or mineralocorticoid, receptor is a cytoplasmic steroid hormone receptor Aldosterone acts to increase water and Na+ reabsorption in: kidney distal tubule distal colon sweat glands salivary glands The activated mineralocorticoid receptor probably acts by increasing the number of: Na+ channels on the lumenal surface of epithelia Na+/K+ ATPase on the basal/lateral membranes Transporting Na+ will cause H2O to follow Angiotensin II (activating a G-protein coupled receptor that signals through Gαq) Stimulates aldosterone synthesis |
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Atrial Natriuretic Factor
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Factor (activating its guanylate cyclase receptor)
Inhibits aldosterone synthesis Atrial Natriuretic Factor is secreted from atrial cardiocytes in response to: High blood pressure High blood volume High blood [Na+] It causes vasodilation decreases aldosterone synthesis Decreases renin synthesis Increases renal blood flow and glomerular filtration rate Increases excretion of H2O and Na+ |
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Which hormone stimulates thirst?
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Angiotensin 2 acts in CNS to stimulate thirst.
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How do ACE inhibitors work?
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Angiotensin-converting enzyme inhibitors (also called ACE inhibitors) are medicines that block the conversion of the chemical angiotensin I to a substance that increases salt and water retention in the body (Angiotensin 2). They are found on endothelial cells.
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25. For each of the following hormones, be able to answer the following questions:
α-MSH Vasopressin Atrial natriuretic factor Insulin Glucagon Epinephrine Leptin Adiponectin Growth Hormone Thyroid Hormone Thyroid Releasing Hormone Thyroid Stimulating Hormone 1α,25-dihydroxy vitamin D3 Parathyroid Hormone Calcitonin Renin Angiotensin II Aldosterone How are they synthesized? Where are they secreted? What controls secretion? What receptor(s) do they bind to? What class does the receptor belong to? What signal transduction pathways are activated? What are the biological effects of the hormone, and for those examples we discussed, what is the molecular mechanism of action? |
See the chart dude.
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